Masonry Facade Water Intrusion - Introductory Paragraph
updated last on December 17, 2010 by Nicholas Simmons
Architectural Engineering Master of Science student at Penn State University. Expected graduation of December 2011.
Masonry units have proven to be a highly durable building material. However, the performance of a masonry wall also relies on the quality of the mortar as well as the design and craftsmanship of the wall and joints. Any weakness is vulnerable to water infiltration and moisture which are often problematic. There are several solutions to reduce the amount of water that enters a building or damages the wall system. However, problems still arise due to the complexity of detailing and constructing the wall system.
Basic Information
Location: State College and Philadelphia, PA along with various other locations throughout the U.S.
Dates: 1900's to current
Type of building: Masonry facade systems for various types of building purposes
Typical cause of failure (water intrusion): Absorption of water through the masonry surface, cracks, joints, and openings is allowed to pass through and can sometimes be trapped and eventually drains to the interior.
Masonry wall components
Masonry wall construction consists of wythes or layers of masonry units. These masonry units are typically stone, brick, or concrete block. Older traditional mass masonry walls were a single wythe, meaning they were made of only one layer. Modern systems are a double wythe which has two layers with an air cavity in the middle. This air pocket increases the overall insulation resistance of the wall system. Another advantage of the double wythe system is that it provides a backup system for preventing water infiltration. Figure 1 shows a typical double wythe system which has bricks (red) as the outside wythe. A few bricks have been removed to expose the inside wythe which is concrete block (grey).
Figure 1 - Double wythe system. Henderson Building 2010 (Photo by Author)
Figure 2 shows a cross section of a wall system with an outer brick wythe and an inner concrete masonry unit (CMU) wythe. The brick wythe is supported by the CMU wythe with wall ties spaced regularly and shelf angles above openings. In between the wythe is an air space and insulation. A drainage system is incorporated since water is expected to infiltrate past the brick wall. Weep vents allow water in the cavity to return back to the outside. At the shelf angle metal drip edges and sealant are used to prevent water from continuing farther down or to soak into the CMU wythe. There are numerous alterations to this wall section which may be for structural, insulation, and/or water proofing needs. A vapor barrier could be added within the cross section. Flashing could also be used near the roof or ground level and would not be seen in this cross section.
Figure 2 - Wall cross section at shelf angle (Photo courtesy of International Masonry Institute)
The rest of this section covers the basic purposes of these materials. The following section discusses how these components can become susceptible to failure.
Wall Ties
Figure 3 - Masonry ties (from google image search) www.qwikfixings.com
Ties are the anchors that connect the outer wythe or masonry facade to its support. Figure 1 and 2 shows a double wythe wall system which has a CMU wall as the support for the brick wall facade. Note that gravity and lateral loads could be supported by the CMU wall or another system such as a steel frame if properly connected. In either case the anchors are important because they transfer wind lateral load on the outer wythe to the inner wythe. Figure 3 shows a wall system with ties between the inner and outer wythes which are both CMU blocks. During construction these anchors are laid within the mortar bed joint of the inner wythe. Part of the anchor extends out to where the outer wythe will be laid. The ties shown in figure 3 are relatively simple to other types. More sophisticated types allow for adjustment up, down, left, and right. This eases the placement of ties wall in the outer wythe and allows for the movement of the wall due to loads, thermal expansion and contraction, etc. The spacing must be checked to assure that the lateral loads are transferred uniformly. Otherwise excessive deflections will occur in some areas causing cracking within the wall.
Shelf Angles
The majority of the dead load of the outer wythe is carried by itself. However, openings for windows and doors disrupt this load path. Shelf angles distribute the dead load of the wall system to a structural element such as a beam. A shelf angle is shown in figure 2.
Lintel
A lintel may be used instead of a shelf angle. A loose laid lintel is not attached to the back-up structure and thus moves with the outer wythe. The lintel transfers the dead load of the wall above it to the piers on each side of the opening (Farmer 2010 pp 12).
Insulation is essential in most wall systems, however it is not always desired. Insulation comes in numerous types. A rigid
insulation board or a soft insulation batting are quite popular (Figure 4 and 5).
A masonry veneer with steel stud backup has insulation either within the stud space or the cavity. If the insulation is within the stud space a continuous insulation may also be used in front of the sheathing (Krogstad 2010 pp 5 - 6).
Movement and Expansion Joints
These joints play a vital role in the serviceability of a masonry wall. "They accommodate movement resulting from intrinsic material properties and exposure to the environment" (Farmer 2010 pp 1). However, if used incorrectly they can reduce the life expectancy of the structure. Most masonry walls require movement joints, but only some require expansion joints. Note some sources may refer to movement joints as control joints or expansion joints. This section refers to a movement joint as a joint within only the wall. An expansion joint continues throughout the cross section of the building including the floors, roof, and structural framing system.
Movement joints can be either horizontal or vertical to accommodate movement in the perpendicular direction. Movement within the wall may be caused by thermal changes, moisture changes, differential movements, shrinkage, or deformation (Farmer 2010 pp 2). The thermal and moisture changes are mostly reversible. They other movements are typically irreversible (Farmer 2010 pp 3). Figure 6 shows that without horizontal joints the brick (outer wythe) will begin to buckle due to compressive forces. Besides dead load, compression of the brick wythe occurs due to temperature increases, concrete shrinkage, and concrete creep (Farmer 2010 pp 4). Lateral loads can further increase the deformed shaped of the buckling brick wythe.
Figure 6 - Vertical expansion of bricks (Photo courtesy of Farmer 2010 / ASTM)
The critical combination should be considered when determining the size, spacing, and location of vertical and horizontal movement joints. Often the joint size is selected to be the same as the typical mortar joint. Other influences on the recommended spacing are the type of sealant, the size of the masonry units and the location of reinforcing steel (Farmer 2010 pp 5-6). For parapet walls the recommended spacing is half of that for the wall below it. This accommodates the additional volume change since the parapet is exposed on three sides and the wall below is exposed on only one side. The location of vertical joints should be near corners, at material changes within the facade, and at changes in wall structure. Any intermediate joints should be hidden along window openings (Farmer 2010 pp 8). For windows more than six feet wide a joint should be placed on both sides of it (Farmer 2010 pp 12). Horizontal joints should be placed at backup supports such as floor slabs, precast concrete, or shelf angles (Farmer 2010 pp 9).
If loose laid lintels are used then a vertical movement joint may not just simply be along the edge of the window. The joint would not be effective since it would be intersected by the lintel. There are two solutions. One is to place a bond break below the lintel bearing (Figure 7 left). A soft flexible joint must be installed in front of the lintel and adjacent to it. Any differential movement between the lintel and the brick can be accommodated without damage to the brickwork. The other option is to relocate the movement joint to the center of the pier as shown in Figure 7 right (Farmer 2010 pp 12-14).
Figure 7 - Movement joint solution for loose laid lintels. Bond break (left) and relocated joint (right) (Courtesy of Farmer 2010 / ASTM)
Movement joints must terminate at an opening or at the end of the wall section. They must not be interrupted or terminate into a solid.
A fenestration refers to an opening in the wall system for a window, door, etc. The fenestration system refers to the framing around that opening, how it connects to the wall for support, and any water proofing materials. The fenestration system should be positioned to center the thermal break to be within the plane of the insulation in the surrounding wall. Since this is not always practical, at least a portion of the fenestration system frame should be within the plane of the insulation. It should not be completely in the plane of the masonry veneer (Krogstad 2010 pp 6).
Vapor, Water, and Air Barriers
The use of any of these barriers depends on the design of wall system and the environmental conditions.
Vapor barriers are used when condensation is expected to occur within the cavity wall system. The vapor barrier controls where the condensation occurs so that it can then be properly managed and drained out to the exterior. Some vapor barriers are not completely impermeable and thus are referred to as vapor retarders. Vapor retarders may be practical in northern climates (Krogstad 2010 pp 6).
Water resistive barriers can be used in a cavity wall system to stop mortar bridges from transferring moisture into the inner wythe. This must be properly installed against the face of sheathing, sealed at floor lines, integrated with flashing, and be without tears. Water bridging across the mortar will be directed down the wall and then drains to the exterior at the through-wall flashing. The water barrier in this case also acts as an air barrier. The barrier may also be designed as a vapor barrier (Krogstad 2010 pp 2).
Flashing
Flashing is an important detail in wall construction. The basic concept of flashing is to direct water away from the wall's most vulnerable areas and towards some sort of drainage. Typically locations for flashing is at the parapet wall and above fenestrations. Copper and stainless steel are both excellent materials to use because they match the durability and longevity of masonry itself. They are puncture and tear resistant which is key to withstanding the rigors of installation. They are resistant to the sun's ultraviolet rays. They can be installed at any temperature unlike rubberized asphalt which requires a range of 25° to 100° F (Subasic 2001 pp 30). Unlike many rubber, plastic, and asphalt based flashing, copper and stainless steel are compatible with most common sealants and caulks. They are both corrosion resistant (Subasic 2001 pp 31). Copper and stainless steel flashing may be mechanically keyed along the length to create a stronger mechanical bond to the mortar of the wall (Subasic 2001 pp 34).
Comparison table based on (Subasic 2001 pp 34).
Flashing Material
Advantages
Disadvantages
Material Costs*
Stainless steel, Type 304, 26 gauge
Durable, impervious hard
Difficult to bend, form, and solder
$2.50-$3.35/lin. ft.
Cold-rolled copper
Durable flexible, impervious, easy to form and solder
Stains surfaces where water runs off; damage by excessive flexing
$2.50-$3.35/lin. ft.
Lead-coated copper, 16 oz
Same as copper; does not stain, easy to paint
Damaged by excessive flexing; requires special care to solder
$4.75/lin. ft.
Mill-galvanized steel 26 gauge
Hard , impervious, easily formed, easy to paint
Subject to early corrosion in acidic environment; difficult to solder
$1.50/lin. ft.
Copper laminate fabric, 5 oz. (copper sandwiched between asphalt and glass fiber mesh)
Easy to form and join
More easily torn and punctuated then metal; asphat degrades in sunlight
$1.19-$1.47/lin. ft.
Drip edge, stainless steel
Durable; compatible with sealants
Only used in outer wythe
$1.00-$1.50/lin. ft.
*note costs based on 2001 publication
Copper
Copper is both durable and flexible. It may arrive on site as flat sheets or preformed shapes. It can be coated with lead to improve malleability and reduced staining of the wall. Too much bending can damage the flashing. Copper is popular for historic restoration since it often matches the existing materials (Subasic 2001 pp 34). The green patina is associated with copper impurities. Modern copper products have fewer impurities and as a result weather to a dark brown, gray, or black color (Subasic 2001 pp 34).
Stainless Steel
Stainless steel is strong and corrosion resistant but it is difficult to bend and/or weld. This often requires sheet metal workers which needs to be coordinated with the masons. The stainless steel may arrive on site as flat sheets or preformed shapes, but the latter is preferred (Subasic 2001 pp 32). Aesthetically, stainless steel is often preferred for light colored masonry and is avoided for dark colored masonry (Subasic 2001 pp 34).
Through wall flashing
An example of through wall flashing is in Figure 2. A through wall system at a lintel must be properly integrated with the wall including water barriers, if provided. Otherwise leakage can occur behind the lintel (Krogstad 2010 pp 2).
Parapet wall of a flat roof
For a parapet wall a through wall system is best to prevent water from reaching the interior. However, partial systems are sometimes used instead as an alternative which may suffice for some time and has a lower initial cost. Flashing should be located directly underneath the coping and at the bottom of the parapet wall as well. Drip edges should be used to direct water away from contacting the wall again.
End dams for Lintels and Step Flashing An end dam is a flashing which is often a piece of sheet metal with several bends. The backside bend integrates with the inner wythe and water barriers, the front side bend creates a drip edge, the other two sides are bent up to prevent water from traveling laterally. End dams are used above lintels to direct water to the outside and to protect the steel lintel from moisture. Thus the end dam must extend past the lintel (Krogstad 2010 pp 2).
The intersection of a wall with a roof may have water collecting there like a gutter. This makes it vulnerable for water penetration. Thus the flashing detailing is very important. To provide protection where it is needed the flashing must be provided in steps that follow the roof line. An end dam is a type of step flashing. As shown in Figure 8, the end dam is inserted into the mortar joint of the CMU wall to ensure that any water flowing down the cavity must then stop and flow out through the bricks to drain off the roof. This prevents the water from flowing down the cavity and collecting at the bottom which may lead to the inside of the wall or a room below.
Figure 8 - End dam flashing Photo courtesy of Masonry Preservation Services, Inc. (MPS)
Rain Screens
Rain screens are another barrier system used to block the majority of the water from contacting the wall. They are not common to most wall systems. In Figure 9 (left) it appears that the screen is made out of material similar to vinyl siding. Rain screens do not eliminate the need for other water proofing elements such as flashing. As shown in Figure 9 (right), a membrane is adhered to the wall. This would be more effective if the membrane were laid in the mortar joint of the bricks.
Figure 9 - Rain screen (Left) The flashing membrane behind the rain screen (Right) Photo courtesy of Masonry Preservation Services, Inc. (MPS)
Brick, CMU blocks, and mortar can allow water to pass through them at different rates. These rates can be reduced by glazing bricks and incorporating certain admixtures to the concrete for the blocks or mortar. For restoration of pervious walls they should not be re-pointed with modern motar which is impervious. Heat and moisture can then only escape through the brick surface. This can cause extensive damage in five to ten years (Procter 2001 pp 16).
The rate at which water permeates through a wall system depends on both the materials used and how they are interconnected. Most studies have developed the characteristics of the individual materials. However, there is significantly less known about the overall effects of composite layers, material interfaces, and overlap lengths. Variance in the detailing of the wall section can affect the overall water vapor diffusion and air permeance (Hens 2006 pp 745). As a result, the overall behavior cannot be predicted just by the properties of the subcomponents, but rather experimental testing is required.
Capillary effect and surface tension
Capillary effect and surface tension are properties of water that are often confused with each other. The phenomenon of the capillary effect occurs in part due to surface tension. To the left is a video that shows the capillary effect of water moving against gravity from a source through a medium into another container. Capillary effect can occur when water is in contact with the base of a wall (Figure 10). The water may travel up the wall on the outside surfaces of it, however the capillary effect tends to be stronger in between the wythes where there is more surface area of material. The capillary effect also occurs on outside face of the outer wythe during a rain event. Rain water that hits the side of the wall will either enter into the face of the brick or the mortar joint. The capillary effect will then push the water to travel deeper into the wall.
Back in the early 1900's moisture damage was starting to be considered a serious issue. The first solution was an admixture to mortar to reduce capillarity. After the 1920's cement mortars became more popular than lime mortars. This increased the need for waterproofing (Thayer 1947 pp 911). The early admixtures where metallic or fatty acid based (Thayer 1947 pp 912). For more modern times, the capillary suction can be improved with integral water-repellent (IWR) admixtures (Karkare and Walloch 1996). For a one hour test of NCMA brick the amount of water absorbed through a 30si area was reduced from 65g to 3.9g by adding 60 oz of IWR admixture / cwt cement (Karkare and Walloch 1996). The water uptake rate was reduced by 86% for brick and 85% for mortar. The most effective amounts of IWR are considered to be 25-30 oz/cwt for the NCMA brick with a reduction of 86%; and 24-32 oz/cwt for the PC/L Type S mortar made with standard sands had a reduction of 86% (Karkare and Walloch 1996).
Figure 10 - Capillary action at ground (from google image search) www.buildingscience.com
Another permeance factor is the clear water repellent (CWR), if any, that is applied to the outside surface (Greenwald 2008 pp 2). Ten CWR's were tested by Greenwald's experiment on single wythe CMU walls. Each wall system was tested first without CWR, then tested again after a CWR was applied, then each wall was aged for a year outside and tested a third time. The majority of walls tested resisted water better with a CWR than without. The best performing CWRs were solvent-based as opposed to water-based or alcohol-based. All of the walls performed significantly better when aged a year outside (Greenwald 2008 pp 8). This may not always be the case if detrimental effects such as cracking or spalling occur. Greenwald also compared the effects of the light-weight and normal-weight masonry units. Prior to the application of the CWR, the normal-weight walls leaked about 30% less than the light-weight walls (Greenwald 2008 pp 9).
Similar to admixtures, glazing for bricks were first being used in the early 1900's. Brick glazing forms an impervious level that does not allow water in. It offers a wide selection of appearances, is durable, stain resistant, and easy to maintain (Gorrell 2007 pp 1). Its primary purpose is its resistance against allowing water to flow through it. However this also made it susceptible to deterioration, as later discussed. Follow this link.
Internal pressure and humidity from HVAC
The influences of an Heating, Ventilating, and Air Conditioning (HVAC) system may change the rate at which moisture moves through a wall. High humidity inside the building combined with the heat of the sun will draw moisture through the wall to the outside. This will cause efflorescence on the outside surface (Thayer 1947 pp 912). Efflorescence could occur on the inside surface if the inside temperature were higher and the humidity lower than that of the outside. This often leaves a fine white powder on the plaster around the windows (Thayer 1947 pp 912). The HVAC system may also change the air leakage patterns of a building. Under neutral pressure the stack effect leads to air escaping from the top floor of a building. With positive pressure the air begins to escape out around window openings. This increase in air movement carries moisture which collects in the cladding surrounding windows (Colantonio 2005 pp 177).
Note that other causes of efflorescence will be discussed later and shown in Figure 15.
Condensation
Warm moist air will tend to flow into a wall system from the outside during the summer or from the inside during the winter. The thermal resistance of the wall then creates a thermal gradient. Condensation may occur within the wall system where ever it is below the dew point temperature. Typically this occurs at the first surface that the moisture contacts that is below the dew point temperature. However, a vapor barrier can be introduced at a desired location for condensation to occur and be drained to the outside (Krogstad 2010 pp 3). Thermal bridging of steel support angles, masonry returns, sill covers, flashing, and anchorage clips can cause localized condensation which may not be covered by the drainage system (Krogstad 2010 pp 4). To reduce the flow of moist air into the cavity, it should be sealed as best as possible. The air/water barrier around fenestration systems should also be sealed (Krogstad 2010 pp 3-4).
Interfaces of veneer system - failures
Figure 11 - Bad flashing and sealant protection (Photo by Author)
A common source of excessive water infiltration is the misuse or the lack of the building materials such as flashing, sealants, and movement joints. Sometimes the materials are installed correctly, but over time they wear down and then perform poorly (Farmer 2010 pp 1). However, many times the cause is the improper detailing at the interface of the masonry veneer with either openings or other cladding. Anchorage between these systems can penetrate through flashing (Krogstad 2010 pp 1-2). Figure 11 shows that the flashing at the top of the masonry wall does not provide much protection. There is a drip edge, but it does not appear to have a significant overhang. If there was a sealant it has worn away. The flashing or membrane shown above the top layer of bricks, is not integrated properly to prevent water from traveling down into the bricks or into the cavity.
Aesthetics and safety can be impacted by water entering into the building. It can deface the veneer of a building with spalling and stains. Moisture within the wall system can cause steel to rust which leads to cracks which also leads to more water infiltration. Moisture that reaches the interior can stain or enhance mold growth on the interior finishes. Mold is also a health hazard to any occupants.
Mortar Washout and Cracks
Figure 12 - Mortar washout. Photo courtesy of Masonry Preservation Services, Inc. (MPS)
Washout of the mortar and cracks are a clear sign of the wall system beginning to break down. They pose a serious issue of allowing water to flow into the wall cavity or directly into the building. This will lead to acceleration of the wall deterioration. In turn this may lead to more damage of the wall. Figure 12 shows mortar that has washed out. The lack of mortar poses another serious issue of loose bricks falling out.
Cracks may form due to a few reasons such as expansion and contraction of the wall. In colder climates the freeze thaw cycle gradually breaks down the surfaces of the wall. In southern climates the rapid changes in temperature can be just as serious, especially for the south and east elevations (Thayer 1947 pp 911). If movement joints are not sized and spaced appropriately then high stresses within the wall will lead to cracks.
Another cause of cracks is the corrosion or oxidation of steel which occurs in the presence of moisture. During corrosion the steel expands and applies pressure to any material it is in contact with. Some examples are the reinforcing steel in concrete or masonry units; the flanges of embedded steel sash; angles or channels embedded to hold door frames; I-beams, H-columns, and lintels encased in concrete; supports for motors, tracks, etc. (Thayer 1947 pp 912). A clear sign that there is moisture moving in and out or through the wall is efflorescence which will be discussed later and is shown in Figure 16.
Figures 13 and 14 show cracks that have formed around window openings. These could have formed from the shelf angles rusting.
Figure 13 - Carnegie Building: Cracking of lintels (left) and after a repair attempt (right) Location Penn State, University Park, PA (Photo by Author)
Figure 14 - Cracking of window sill on the Weaver Building (left) and the Engineering Unit A (right) Location Penn State, University Park, PA (Photo by Author)
Another cause of cracks is non-uniform settlement of the building. A typical indication of this is that the crack width is largest at one end and is closing at the other end. For example if the right half of a wall has settled more than the left hand half, then the crack will likely be vertical and is largest at the top and closing at the bottom.
Spalling
Figure 15 - Spalling of exterior brick wall. (Photo found on google search) www.multiguard-solutions.com
Spalling refers to any portion of a wall system falling off. Often this refers to blocks or bricks of the outer wythe becoming loose and then falling to the ground. This process usually due to a freeze / thaw cycle of moisture on the inside the wall system. Pressure is exerted outward on the wall and the mortar around the blocks or bricks either cracks or washes out. Figure 15 shows that the face of the brick has spalled off. If the brick has a glazing then the spalling is likely due to moisture entering the wall and become trapped by the glazing on the exterior face (Gorrell 2007 pp 1). Brick glazing forms an impervious level that does not allow water in. However it also does not allow water to escape that has entered through other means such as mortar joints, cracks, failed sealant joints, failed flashing, and failed coping (Gorrell 2007 pp 1-2). The freeze / thaw cycle of the moisture trapped inside the brick, may then cause the glazing to spall off of the brick. In this case the spalling is aesthetically displeasing and it may also be hazardous when larger pieces spall off.
Efflorescence
Figure 16 - Efflorescence and erosion of the window lintels (top left of photo) Engineering Units A and B. Location Penn State, University Park, PA (Photo by Author)
Figure 16 shows a few problems with the envelope of this building. The left side of the figure shows a white stain on the wall which is efforescence. The efflorescence is likely the result of moisture penetrating from the outside then being drawn out by the heat of the sun (Thayer 1947 pp 911). The erosion of the stone lintels about the windows suggests that water is running down the side of the building. This could be occurring due to a poorly designed runoff system, a clogged gutter, flashing failure, etc.
Freeze / thaw damages
Figure 17 - Failure of roof flashing Photo courtesy of Masonry Preservation Services, Inc. (MPS)
As previously mentioned, the freeze / thaw occurs when a the system has failed to keep moisture out. The damage from the cycle often accelerates the rate at which moisture may enter a building. Some other freeze / thaw damages that occur are shown in figures 17 and 18. Figure 17 shows that the roof flashing has failed. Through the scope of this wiki is the masonry wall, it is still important to consider the roof. Rainwater that is improperly drained from the roof could be a possible source of water intrusion into the wall system. The roof flashing appears to be easily pulled up. This suggests that it was not properly integrated with the waterproofing membrane. If this occurrence is near the wall system there is little chance of another barrier system to prevent water from entering the masonry wall or the rest of the building.
Figure 18 - Failure of parapet flashing / lack of one Photo courtesy of Masonry Preservation Services, Inc. (MPS)
Figure 18 shows a closeup of a parapet wall failure. A through wall flashing was not provide. This allowed moisture into the parapet which was then impacted by a freeze / thaw cycle. In addition the improper movement joint design for the parapet wall has allowed a buildup of stress to cause layers of bricks to buckle upwards. Due to this failure the parapet wall is not significantly protecting the wall below from water entering.
The type of repair work often depends on the extent of the damage and the cause. If the damage was the result of a misplaced movement joint, then at the location of new movement joints should be placed as discussed previously. If the extent of brick replacement is to be minimized then the movement joint should be located where significant cracks have formed. Prior to installing new joints, the lateral support of the proposed altered wall must be verified. Installing new joints can rapidly release stresses which might cause crushing, cracking, and instability of the masonry (Farmer 2010 pp 15-16).
A lack of movement joints should not cause problems in older masonry with multiple wythes. The wall can better redistribute stresses from volume changes due to having more mass. The larger dead load also increases the shear resistance against horizontal movement. It is thus unwarranted and also difficult to install movement joints (Farmer 2010 pp 14).
Over the lifetime of a masonry wall it may experience net growth due to the effects of irreversible movement of the wall mentioned earlier. Thus joint widening can be anticipated as routine maintenance for some wall systems (Farmer 2010 pp 18).
The most common procedure for repairing the facade is replacement. It is sometimes better to replace entire sections of the wall system rather then just the damaged area. Whereas replacing just the damaged bricks can be tedious and challenging to patch up in an aesthetic way. Figure 19 shows a masonry arch wall that had to be entirely replaced including the steel lintel. If the flashing is missing or is improperly placed then large sections of the wall must be removed to allow for the installation of new materials.
Figure 19 - deterioration of a masonry arch wall (left) and repair (right) photos courtesy of Masonry Preservation Services, Inc. (MPS)
Gorrell presents a case study of a 1960’s building 35’ tall, 220’ wide, and 540’ long which has a failure of its glazed brick veneer. Brick spalling was significant at the parapet wall and just below it. The parapet had a 12” cavity. The interior parapet wall is 6” concrete masonry backup with 4” brick. The exterior parapet wall is 4” concrete masonry backup with 4” brick (Gorrell 2007 pp 2). The coping did not provide a drip edge. A repair effort was made in the 1980's and some of the bricks were replaced. The movement joint was spaced about every 36’ and was stepped to follow the mortar joints of the bricks. The movement joints were not located near the corners of the building. The sealant used was over stretched and sealant was also used poorly to repair cracks (Gorrell 2007 pp 3). The flashing beneath the coping was missing. The flashing at the bottom of the parapet was cracked and did not typically extend to the outside. The wall ties were severely corroded. The roof had an irrigation system which inadvertently would spray on the parapet wall. This further increased the amount of water entering into the wall system (Gorrell 2007 pp 4). This shows an example of an unsatisfactory repair effort. The new restoration plan was then prepared and executed. The wall system was completely removed and rebuilt. The focus of the design was to prevent water infiltration, allow for quick drainage, and provide ventilation. Ties and bricks were also replaced for the wall below. The new design allowed for a 2” cavity between the facade and masonry backup to prevent blockages from mortar droppings (Gorrell 2007 pp 4). Glazed bricks shall be detailed to comply with ASTM C 1405 and BIA Technical Note 13 “Ceramic Glazed Brick Exterior Walls.” (Gorrell 2007 pp 9).
The first section covered the various components and variances that can be combined to create countless unique masonry walls. Many of the components are intended to prevent water from entering into the building. However, each one has failure modes which could then allow water or moisture in. These failure modes can often be classified as improper design, improper installation, or aging of the materials. A failure at one location may allow moisture in which may then cause damage such as spalling due to freeze / thaw cycles or metals rusting. This damage often leads to an increase in water infiltration as well as infiltration at new locations. Integrating the materials together is one of the most challenging aspects to a good design for a masonry wall to resist water entering the building. It is difficult to determine how well a wall will perform considering only the properties of the materials. Experimental testing is appropriate, since the interconnections are often the weak points.
Restoration of a failed wall system is unique to each wall system. This makes this difficult to generalize an example for this discussion. and This is also difficult for the owner if a particular solution is the best solution for his interests. Thus, at least two alternatives for remediation should be presented to the owner including the benefits and drawbacks of each. One remediation solution sould represent the minimal amount of work that is required. This option will hopefully be economical, but does not provide the best protection against future issues. Consider a general case of a masonry cavity wall system that has cracks caused by a lack of or improper spacing of movement joints and additional damage caused to the bricks by water intrusion.
The first option would integrate new flashing, install movement joints, improve the drainage system, and replace bricks within a small range of where damage was noticed. The drawbacks to this option is that it may be more difficult to integrate the new flashing with the existing flashing at the edges of the scope of work. This could lead to water intrusion and resulting damages which lead to higher maintenance costs and/or another rehabilitation effort. Also, matching the color and texture of the new bricks with the old bricks may be difficult and become noticeable patchwork.
The other option should be the most complete and through. This option will most likely to have the highest initial cost, but it should offer the best protection against future issues and thus future expenses. For the same example, this option would require large sections of the wall to be replaced. This would allow for better craftsmanship and consistency of the new flashing, movement joints, and drainage. Due to the difficult in matching color and texture of bricks, this method would allow for any aesthetic differences to be better hidden. As needed, alternatives should be provided that are in between these two extremes to best fit the owners interests.
Envelope Failure Case Studies
Henderson Connecting Link Facade
Location at Penn State, University Park, PA (Photos by Author)
Click here to view the report
Colantonio, Antonio, and Garry Desroches. (2005). "Thermal patterns on solid masonry and cavity walls as result of positive and negative building pressures." Paper presented at Thermosense XXVII, March 29, 2005 - March 31, , http://dx.doi.org/10.1117/12.606000.
Moisture accumulates within wall assemblies from the moisture in air moving across a temperature gradient. This paper outlines the thermal patterns creased by positive and negative building pressures. These then provide the air flow patterns due to pressure, wind, and the stack effect.
Farmer, Matthew C., and Edward A. Gerns. (May 2010.) "Design and use of expansion joints in new and existing clay masonry wall systems." Journal of ASTM International 7 (5), http://dx.doi.org/10.1520/JAI102864.
This paper clarifies and expands on the standard guidelines for joint placement, size, and spacing. It suggests placement and detailing for atypical situations such as existing buildings, parapets, solid masonry wall systems, and window lintels. Common installation and maintenance problems are addressed.
Gorrell, Todd A., and Ian R. Chin. (2007). "Investigation and repair of glazed brick cladding: A case study." Journal of ASTM International 4 (1), http://dx.doi.org/10.1520/JAI100266.
Water typically enters in through joints even with a glazed brick cladding. However, the glazing then prevents the water from evaporation from the face of the wall. The freezing of trapped moisture then causes spalling. This paper discusses common failure modes, design/detailing recommendations, and a case study including the repair of a spalling wall.
Greenwald, Jeffrey H., and Thomas C. Young. (2008). "Evaluation of the effectiveness of clear water repellent coatings on partially grouted single-wythe concrete masonry walls." Paper presented at 11th Symposium on Masonry, June 13, 2006.
Evaluates clear water repellent coatings. Repellents have grown in number and their chemical composition has changed during recent years. 14 walls were constructed and tested in accordance with ASTM E 514. The walls were tested uncoated, coated, and coated then aged 1 year outside then tested.
Hens, Hugo S. L. C. (June 2006.) "The vapor diffusion resistance and air permeance of masonry and roofing systems." Building and Environment 41 (6): 745-55, http://dx.doi.org/10.1016/j.buildenv.2005.03.004.
Test to measure the vapor diffusion resistance of composite layers. Cavity walls diminish the risk of condensation and helps dry the cladding after rainfall.
Karkare, Milind V., and Craig T. Walloch. (July 1, 1996). "Capillary suction model for concrete masonry and its application to integral water-repellent masonry." Paper presented at Proceedings of the 1995 Symposium on Masonry: Esthetics, Engineering, and Economy, December 5, 1995.
Capillary suction is the main mechanism of water absorbing into a masonry wall. This article proposes a new test method to characterize the capillary suction properties of concrete masonry. water capillary suction data for concrete block and Type S portland cement-lime mortar is presented for varying amounts of integral water-repellent (IWR) admixtures.
Krogstad, Norbert V., Richard A. Weber, and Michael J. Huhtala. (April 1, 2010). "Detailing masonry veneer/steel stud backup systems at fenestration systems to avoid moisture problems." Journal of ASTM International 7 (4), http://dx.doi.org/10.1520/JAI102735.
Over 20 years of water leakage and condensation problems were mostly related to the interface between masonry veneer and fenestration systems. The problems occur with aggressive exposures against inqdeuaately designed or construction drainage and air seals. In many cases drainage systems is not properly installed; air barriers and vapor retarders are not sealed to fenestration systems. Anchors, lintels, support angles, and sill flashings are not thermally improved. Paper outlines detailing the interface. Fenestraction types include typical storefront or operable windows and curtain walls.
Procter, Don. "A Case for Hydraulic Mortar." Masonry Construction, April 2001, 16-22.
Discusses the differences between hydrulic lime mortars and hydrated lime mortars as well as applications for restoration work.
Subasic, Christine A.. "Stainless Steel vs. Copper Flashing." Masonry Construction, April 2001, 30-38.
Discusses the importance of flashing in buildings. It covers the benefits and drawbacks of stainless steel, copper, and a few other options.
Thayer, R. D. (September 1947). "Moisture control in masonry maintenance". Sewage Works Journal 19 (5): 911-4.
Spalling and cracking of concrete and brick; efflorescence of brick and tile; staining of stone and disintegration of mortar joints; rusting of reinforcing rods due to penetration of moisture; surface types of waterproofing materials; penetrating type; resinous material and inorganic silicones
Additional Resources
ASTM E 514 “Standard Test Method for Water Penetration and Leakage Through Masonry.”
Barrett, Peter. (November 1983). "RAIN PENETRATION THROUGH MASONRY WALLS." Insulation Journal (Watford, England) 27 (11): 35,36, 38-39.
Covers the fundamental principals of water infiltration and the ineffectiveness of some cladding examples.
Beall, Christine. (June 1988). "CONTROLLING MOISTURE MOVEMENT IN MASONRY WALLS". Construction Specifier 41 (6): 36,42, 45, 47.
Recommendations for designing in humid climate. Discusses cavity walls, flashing, material selection, waterproofing, dampproofing, condensation, construction of vapor barriers, application of finishes, and controlling moisture movement.
Butt, Thomas K. (2006). "Water resistance and vapor permeance of weather resistive barriers." Paper presented at ASTM E06 Symposium 2004, April 18, 2004.
Weather-resistive barriers (WRBs) resist both water and air passage, but allow moisture movement. This article provides some light to the lack of comparable material properties and selection guilds. Both building code requirements and vendors' product information are inconsistent and confusing.
Conwell, Scott M. (January 1, 2005). "Water-resistant single-wythe masonry walls." Construction Specifier 58 (1): 63-6.
Proper detailing, attention to applicable code requirements, sensitive material selection, and gold workmanship are necessary for wall performance and water resistance.
Demars, Y., and Y. Buck. (1982). "WATER VAPOR DIFFUSION THROUGH INSULATED, MASONRY BUILDING WALLS." Paper presented at Moisture Migration in Buildings. .
Compares theoretical prediction and experimental results. Discusses conventional permeability values and conditions for condensation.
Farmer, Matthew C. (2005). "Traditional brick masonry detailing meets modern cavity wall construction - A difficult marriage." Paper presented at 2005 Structures Congress and the 2005 Forensic Engineering Symposium - Metropolis and Beyond, April 20, 2005 - April 24, 2005.
This paper attempts to identify some critical considerations when traditional aesthetics are applied to modern cavity wall construction. Through exploration of these challenges and their eventual solutions, it is hoped that designers will consider the constructability of desired masonry detailing to help avoid serviceability problems in the future.
Janopaul Jr., Peter. (1999). "Use of polyurethane foam to provide a watertight concrete masonry wall and a sealed connection of the wall to the foundation." ASTM Special Technical Publication(1352): 163-72. The critical elements in perfecting this procedure are the detailing of the base of the wall, with a continuous exterior first course foam side cleanout, then following this detailing in the field construction of the wall, and properly foaming the constructed wall with polyurethane foam. The polyurethane foam must be poured into the foam cavity after the face shells have been replaced at the first course cleanout.
Krogstad, Norbert V., Richard A. Weber, and Dennis K. Johnson. (July 1996). "Common problems at the interface between masonry drainage walls and windows." Paper presented at Proceedings of the 1995 Symposium on Masonry: Esthetics, Engineering, and Economy, December 5, 1995.
Considers how deficiencies at windows can lead to water leakage, water staining, peeling paint, condensation, mold, and mildew. The windows considered include horizontal ribbon, shallow/deeply recessed punched windows, and vertical strip windows. Multi-component flashings are used to prevent thermal bridging, water, and air leakage.
McGinley, W. M., and Denis A. Brosnan. (July 1996). "Water penetration testing of single wythe residential load-bearing clay masonry wall systems." Paper presented at Proceedings of the 1995 Symposium on Masonry: Esthetics, Engineering, and Economy, December 5, 1995.
Summary of investigation including 18 wall specimens using ASTM E 514 Insulation, tie connectors, and moisture barriers were varied to create 6 different configurations. Construction procedures are discussed and recommendations are made for detailing.
O'Connor, T. F., and H. L. Droz. (July 1996). "Design considerations for sealants when used at horizontal expansion joints in masonry cavity walls." ASTM Special Technical Publication(1286): 63-83.
Inadequate considerations of flashing materials and sealant installation conditions let to poor protection against leaks. This paper suggests a tube and plate support design. Deflection, rotation, erection tolerances, and flashing materials are provided.
Olson, Eric K. (February 1, 2005) "Avoiding the perils of paper-faced exterior gypsum sheathing" Construction Specifier58 (2): 65-9.
The threats of mold growth on public health and wall systems are discussed. Varies factors of growth are mentioned. CMU walls are considered as any alternative to prevent mold growth.
Masonry Facade Water Intrusion - Introductory Paragraph
updated last on December 17, 2010 by Nicholas SimmonsArchitectural Engineering Master of Science student at Penn State University. Expected graduation of December 2011.
Table of Contents
Basic Information
Location: State College and Philadelphia, PA along with various other locations throughout the U.S.Dates: 1900's to current
Type of building: Masonry facade systems for various types of building purposes
Typical cause of failure (water intrusion): Absorption of water through the masonry surface, cracks, joints, and openings is allowed to pass through and can sometimes be trapped and eventually drains to the interior.
Masonry wall components
Masonry wall construction consists of wythes or layers of masonry units. These masonry units are typically stone, brick, or concrete block. Older traditional mass masonry walls were a single wythe, meaning they were made of only one layer. Modern systems are a double wythe which has two layers with an air cavity in the middle. This air pocket increases the overall insulation resistance of the wall system. Another advantage of the double wythe system is that it provides a backup system for preventing water infiltration. Figure 1 shows a typical double wythe system which has bricks (red) as the outside wythe. A few bricks have been removed to expose the inside wythe which is concrete block (grey).Figure 2 shows a cross section of a wall system with an outer brick wythe and an inner concrete masonry unit (CMU) wythe. The brick wythe is supported by the CMU wythe with wall ties spaced regularly and shelf angles above openings. In between the wythe is an air space and insulation. A drainage system is incorporated since water is expected to infiltrate past the brick wall. Weep vents allow water in the cavity to return back to the outside. At the shelf angle metal drip edges and sealant are used to prevent water from continuing farther down or to soak into the CMU wythe. There are numerous alterations to this wall section which may be for structural, insulation, and/or water proofing needs. A vapor barrier could be added within the cross section. Flashing could also be used near the roof or ground level and would not be seen in this cross section.
The rest of this section covers the basic purposes of these materials. The following section discusses how these components can become susceptible to failure.
Wall Ties
Shelf Angles
The majority of the dead load of the outer wythe is carried by itself. However, openings for windows and doors disrupt this load path. Shelf angles distribute the dead load of the wall system to a structural element such as a beam. A shelf angle is shown in figure 2.Lintel
A lintel may be used instead of a shelf angle. A loose laid lintel is not attached to the back-up structure and thus moves with the outer wythe. The lintel transfers the dead load of the wall above it to the piers on each side of the opening (Farmer 2010 pp 12).Insulation
Insulation is essential in most wall systems, however it is not always desired. Insulation comes in numerous types. A rigid
insulation board or a soft insulation batting are quite popular (Figure 4 and 5).
A masonry veneer with steel stud backup has insulation either within the stud space or the cavity. If the insulation is within the stud space a continuous insulation may also be used in front of the sheathing (Krogstad 2010 pp 5 - 6).
Movement and Expansion Joints
These joints play a vital role in the serviceability of a masonry wall. "They accommodate movement resulting from intrinsic material properties and exposure to the environment" (Farmer 2010 pp 1). However, if used incorrectly they can reduce the life expectancy of the structure. Most masonry walls require movement joints, but only some require expansion joints. Note some sources may refer to movement joints as control joints or expansion joints. This section refers to a movement joint as a joint within only the wall. An expansion joint continues throughout the cross section of the building including the floors, roof, and structural framing system.Movement joints can be either horizontal or vertical to accommodate movement in the perpendicular direction. Movement within the wall may be caused by thermal changes, moisture changes, differential movements, shrinkage, or deformation (Farmer 2010 pp 2). The thermal and moisture changes are mostly reversible. They other movements are typically irreversible (Farmer 2010 pp 3). Figure 6 shows that without horizontal joints the brick (outer wythe) will begin to buckle due to compressive forces. Besides dead load, compression of the brick wythe occurs due to temperature increases, concrete shrinkage, and concrete creep (Farmer 2010 pp 4). Lateral loads can further increase the deformed shaped of the buckling brick wythe.
The critical combination should be considered when determining the size, spacing, and location of vertical and horizontal movement joints. Often the joint size is selected to be the same as the typical mortar joint. Other influences on the recommended spacing are the type of sealant, the size of the masonry units and the location of reinforcing steel (Farmer 2010 pp 5-6). For parapet walls the recommended spacing is half of that for the wall below it. This accommodates the additional volume change since the parapet is exposed on three sides and the wall below is exposed on only one side. The location of vertical joints should be near corners, at material changes within the facade, and at changes in wall structure. Any intermediate joints should be hidden along window openings (Farmer 2010 pp 8). For windows more than six feet wide a joint should be placed on both sides of it (Farmer 2010 pp 12). Horizontal joints should be placed at backup supports such as floor slabs, precast concrete, or shelf angles (Farmer 2010 pp 9).
If loose laid lintels are used then a vertical movement joint may not just simply be along the edge of the window. The joint would not be effective since it would be intersected by the lintel. There are two solutions. One is to place a bond break below the lintel bearing (Figure 7 left). A soft flexible joint must be installed in front of the lintel and adjacent to it. Any differential movement between the lintel and the brick can be accommodated without damage to the brickwork. The other option is to relocate the movement joint to the center of the pier as shown in Figure 7 right (Farmer 2010 pp 12-14).
Movement joints must terminate at an opening or at the end of the wall section. They must not be interrupted or terminate into a solid.
Up to date information on brick walls can be obtained here http://www.gobrick.com/index.cfm or www.bia.org .
Fenestration System
A fenestration refers to an opening in the wall system for a window, door, etc. The fenestration system refers to the framing around that opening, how it connects to the wall for support, and any water proofing materials. The fenestration system should be positioned to center the thermal break to be within the plane of the insulation in the surrounding wall. Since this is not always practical, at least a portion of the fenestration system frame should be within the plane of the insulation. It should not be completely in the plane of the masonry veneer (Krogstad 2010 pp 6).Vapor, Water, and Air Barriers
The use of any of these barriers depends on the design of wall system and the environmental conditions.Vapor barriers are used when condensation is expected to occur within the cavity wall system. The vapor barrier controls where the condensation occurs so that it can then be properly managed and drained out to the exterior. Some vapor barriers are not completely impermeable and thus are referred to as vapor retarders. Vapor retarders may be practical in northern climates (Krogstad 2010 pp 6).
Water resistive barriers can be used in a cavity wall system to stop mortar bridges from transferring moisture into the inner wythe. This must be properly installed against the face of sheathing, sealed at floor lines, integrated with flashing, and be without tears. Water bridging across the mortar will be directed down the wall and then drains to the exterior at the through-wall flashing. The water barrier in this case also acts as an air barrier. The barrier may also be designed as a vapor barrier (Krogstad 2010 pp 2).
Flashing
Flashing is an important detail in wall construction. The basic concept of flashing is to direct water away from the wall's most vulnerable areas and towards some sort of drainage. Typically locations for flashing is at the parapet wall and above fenestrations. Copper and stainless steel are both excellent materials to use because they match the durability and longevity of masonry itself. They are puncture and tear resistant which is key to withstanding the rigors of installation. They are resistant to the sun's ultraviolet rays. They can be installed at any temperature unlike rubberized asphalt which requires a range of 25° to 100° F (Subasic 2001 pp 30). Unlike many rubber, plastic, and asphalt based flashing, copper and stainless steel are compatible with most common sealants and caulks. They are both corrosion resistant (Subasic 2001 pp 31). Copper and stainless steel flashing may be mechanically keyed along the length to create a stronger mechanical bond to the mortar of the wall (Subasic 2001 pp 34).
Comparison table based on (Subasic 2001 pp 34).
Copper
Copper is both durable and flexible. It may arrive on site as flat sheets or preformed shapes. It can be coated with lead to improve malleability and reduced staining of the wall. Too much bending can damage the flashing. Copper is popular for historic restoration since it often matches the existing materials (Subasic 2001 pp 34). The green patina is associated with copper impurities. Modern copper products have fewer impurities and as a result weather to a dark brown, gray, or black color (Subasic 2001 pp 34).Stainless Steel
Stainless steel is strong and corrosion resistant but it is difficult to bend and/or weld. This often requires sheet metal workers which needs to be coordinated with the masons. The stainless steel may arrive on site as flat sheets or preformed shapes, but the latter is preferred (Subasic 2001 pp 32). Aesthetically, stainless steel is often preferred for light colored masonry and is avoided for dark colored masonry (Subasic 2001 pp 34).Through wall flashing
An example of through wall flashing is in Figure 2. A through wall system at a lintel must be properly integrated with the wall including water barriers, if provided. Otherwise leakage can occur behind the lintel (Krogstad 2010 pp 2).Parapet wall of a flat roof
For a parapet wall a through wall system is best to prevent water from reaching the interior. However, partial systems are sometimes used instead as an alternative which may suffice for some time and has a lower initial cost. Flashing should be located directly underneath the coping and at the bottom of the parapet wall as well. Drip edges should be used to direct water away from contacting the wall again.End dams for Lintels and Step Flashing
An end dam is a flashing which is often a piece of sheet metal with several bends. The backside bend integrates with the inner wythe and water barriers, the front side bend creates a drip edge, the other two sides are bent up to prevent water from traveling laterally. End dams are used above lintels to direct water to the outside and to protect the steel lintel from moisture. Thus the end dam must extend past the lintel (Krogstad 2010 pp 2).
The intersection of a wall with a roof may have water collecting there like a gutter. This makes it vulnerable for water penetration. Thus the flashing detailing is very important. To provide protection where it is needed the flashing must be provided in steps that follow the roof line. An end dam is a type of step flashing. As shown in Figure 8, the end dam is inserted into the mortar joint of the CMU wall to ensure that any water flowing down the cavity must then stop and flow out through the bricks to drain off the roof. This prevents the water from flowing down the cavity and collecting at the bottom which may lead to the inside of the wall or a room below.
Rain Screens
Rain screens are another barrier system used to block the majority of the water from contacting the wall. They are not common to most wall systems. In Figure 9 (left) it appears that the screen is made out of material similar to vinyl siding. Rain screens do not eliminate the need for other water proofing elements such as flashing. As shown in Figure 9 (right), a membrane is adhered to the wall. This would be more effective if the membrane were laid in the mortar joint of the bricks.Back to the top of page
Causes of water infiltration
Porosity of masonry and mortar
Brick, CMU blocks, and mortar can allow water to pass through them at different rates. These rates can be reduced by glazing bricks and incorporating certain admixtures to the concrete for the blocks or mortar. For restoration of pervious walls they should not be re-pointed with modern motar which is impervious. Heat and moisture can then only escape through the brick surface. This can cause extensive damage in five to ten years (Procter 2001 pp 16).The rate at which water permeates through a wall system depends on both the materials used and how they are interconnected. Most studies have developed the characteristics of the individual materials. However, there is significantly less known about the overall effects of composite layers, material interfaces, and overlap lengths. Variance in the detailing of the wall section can affect the overall water vapor diffusion and air permeance (Hens 2006 pp 745). As a result, the overall behavior cannot be predicted just by the properties of the subcomponents, but rather experimental testing is required.
Capillary effect and surface tension
Capillary effect and surface tension are properties of water that are often confused with each other. The phenomenon of the capillary effect occurs in part due to surface tension. To the left is a video that shows the capillary effect of water moving against gravity from a source through a medium into another container. Capillary effect can occur when water is in contact with the base of a wall (Figure 10). The water may travel up the wall on the outside surfaces of it, however the capillary effect tends to be stronger in between the wythes where there is more surface area of material. The capillary effect also occurs on outside face of the outer wythe during a rain event. Rain water that hits the side of the wall will either enter into the face of the brick or the mortar joint. The capillary effect will then push the water to travel deeper into the wall.
Back in the early 1900's moisture damage was starting to be considered a serious issue. The first solution was an admixture to mortar to reduce capillarity. After the 1920's cement mortars became more popular than lime mortars. This increased the need for waterproofing (Thayer 1947 pp 911). The early admixtures where metallic or fatty acid based (Thayer 1947 pp 912). For more modern times, the capillary suction can be improved with integral water-repellent (IWR) admixtures (Karkare and Walloch 1996). For a one hour test of NCMA brick the amount of water absorbed through a 30si area was reduced from 65g to 3.9g by adding 60 oz of IWR admixture / cwt cement (Karkare and Walloch 1996). The water uptake rate was reduced by 86% for brick and 85% for mortar. The most effective amounts of IWR are considered to be 25-30 oz/cwt for the NCMA brick with a reduction of 86%; and 24-32 oz/cwt for the PC/L Type S mortar made with standard sands had a reduction of 86% (Karkare and Walloch 1996).
Another permeance factor is the clear water repellent (CWR), if any, that is applied to the outside surface (Greenwald 2008 pp 2). Ten CWR's were tested by Greenwald's experiment on single wythe CMU walls. Each wall system was tested first without CWR, then tested again after a CWR was applied, then each wall was aged for a year outside and tested a third time. The majority of walls tested resisted water better with a CWR than without. The best performing CWRs were solvent-based as opposed to water-based or alcohol-based. All of the walls performed significantly better when aged a year outside (Greenwald 2008 pp 8). This may not always be the case if detrimental effects such as cracking or spalling occur. Greenwald also compared the effects of the light-weight and normal-weight masonry units. Prior to the application of the CWR, the normal-weight walls leaked about 30% less than the light-weight walls (Greenwald 2008 pp 9).
Similar to admixtures, glazing for bricks were first being used in the early 1900's. Brick glazing forms an impervious level that does not allow water in. It offers a wide selection of appearances, is durable, stain resistant, and easy to maintain (Gorrell 2007 pp 1). Its primary purpose is its resistance against allowing water to flow through it. However this also made it susceptible to deterioration, as later discussed. Follow this link.
Internal pressure and humidity from HVAC
The influences of an Heating, Ventilating, and Air Conditioning (HVAC) system may change the rate at which moisture moves through a wall. High humidity inside the building combined with the heat of the sun will draw moisture through the wall to the outside. This will cause efflorescence on the outside surface (Thayer 1947 pp 912). Efflorescence could occur on the inside surface if the inside temperature were higher and the humidity lower than that of the outside. This often leaves a fine white powder on the plaster around the windows (Thayer 1947 pp 912). The HVAC system may also change the air leakage patterns of a building. Under neutral pressure the stack effect leads to air escaping from the top floor of a building. With positive pressure the air begins to escape out around window openings. This increase in air movement carries moisture which collects in the cladding surrounding windows (Colantonio 2005 pp 177).
Note that other causes of efflorescence will be discussed later and shown in Figure 15.
Condensation
Warm moist air will tend to flow into a wall system from the outside during the summer or from the inside during the winter. The thermal resistance of the wall then creates a thermal gradient. Condensation may occur within the wall system where ever it is below the dew point temperature. Typically this occurs at the first surface that the moisture contacts that is below the dew point temperature. However, a vapor barrier can be introduced at a desired location for condensation to occur and be drained to the outside (Krogstad 2010 pp 3). Thermal bridging of steel support angles, masonry returns, sill covers, flashing, and anchorage clips can cause localized condensation which may not be covered by the drainage system (Krogstad 2010 pp 4). To reduce the flow of moist air into the cavity, it should be sealed as best as possible. The air/water barrier around fenestration systems should also be sealed (Krogstad 2010 pp 3-4).Interfaces of veneer system - failures
Back to the top of page
Damages from water infiltration
Aesthetics and safety can be impacted by water entering into the building. It can deface the veneer of a building with spalling and stains. Moisture within the wall system can cause steel to rust which leads to cracks which also leads to more water infiltration. Moisture that reaches the interior can stain or enhance mold growth on the interior finishes. Mold is also a health hazard to any occupants.Mortar Washout and Cracks
Washout of the mortar and cracks are a clear sign of the wall system beginning to break down. They pose a serious issue of allowing water to flow into the wall cavity or directly into the building. This will lead to acceleration of the wall deterioration. In turn this may lead to more damage of the wall. Figure 12 shows mortar that has washed out. The lack of mortar poses another serious issue of loose bricks falling out.
Cracks may form due to a few reasons such as expansion and contraction of the wall. In colder climates the freeze thaw cycle gradually breaks down the surfaces of the wall. In southern climates the rapid changes in temperature can be just as serious, especially for the south and east elevations (Thayer 1947 pp 911). If movement joints are not sized and spaced appropriately then high stresses within the wall will lead to cracks.
Another cause of cracks is the corrosion or oxidation of steel which occurs in the presence of moisture. During corrosion the steel expands and applies pressure to any material it is in contact with. Some examples are the reinforcing steel in concrete or masonry units; the flanges of embedded steel sash; angles or channels embedded to hold door frames; I-beams, H-columns, and lintels encased in concrete; supports for motors, tracks, etc. (Thayer 1947 pp 912). A clear sign that there is moisture moving in and out or through the wall is efflorescence which will be discussed later and is shown in Figure 16.
Figures 13 and 14 show cracks that have formed around window openings. These could have formed from the shelf angles rusting.
Another cause of cracks is non-uniform settlement of the building. A typical indication of this is that the crack width is largest at one end and is closing at the other end. For example if the right half of a wall has settled more than the left hand half, then the crack will likely be vertical and is largest at the top and closing at the bottom.
Spalling
Spalling refers to any portion of a wall system falling off. Often this refers to blocks or bricks of the outer wythe becoming loose and then falling to the ground. This process usually due to a freeze / thaw cycle of moisture on the inside the wall system. Pressure is exerted outward on the wall and the mortar around the blocks or bricks either cracks or washes out. Figure 15 shows that the face of the brick has spalled off. If the brick has a glazing then the spalling is likely due to moisture entering the wall and become trapped by the glazing on the exterior face (Gorrell 2007 pp 1). Brick glazing forms an impervious level that does not allow water in. However it also does not allow water to escape that has entered through other means such as mortar joints, cracks, failed sealant joints, failed flashing, and failed coping (Gorrell 2007 pp 1-2). The freeze / thaw cycle of the moisture trapped inside the brick, may then cause the glazing to spall off of the brick. In this case the spalling is aesthetically displeasing and it may also be hazardous when larger pieces spall off.
Efflorescence
Figure 16 shows a few problems with the envelope of this building. The left side of the figure shows a white stain on the wall which is efforescence. The efflorescence is likely the result of moisture penetrating from the outside then being drawn out by the heat of the sun (Thayer 1947 pp 911). The erosion of the stone lintels about the windows suggests that water is running down the side of the building. This could be occurring due to a poorly designed runoff system, a clogged gutter, flashing failure, etc.
Freeze / thaw damages
As previously mentioned, the freeze / thaw occurs when a the system has failed to keep moisture out. The damage from the cycle often accelerates the rate at which moisture may enter a building. Some other freeze / thaw damages that occur are shown in figures 17 and 18. Figure 17 shows that the roof flashing has failed. Through the scope of this wiki is the masonry wall, it is still important to consider the roof. Rainwater that is improperly drained from the roof could be a possible source of water intrusion into the wall system. The roof flashing appears to be easily pulled up. This suggests that it was not properly integrated with the waterproofing membrane. If this occurrence is near the wall system there is little chance of another barrier system to prevent water from entering the masonry wall or the rest of the building.
Figure 18 shows a closeup of a parapet wall failure. A through wall flashing was not provide. This allowed moisture into the parapet which was then impacted by a freeze / thaw cycle. In addition the improper movement joint design for the parapet wall has allowed a buildup of stress to cause layers of bricks to buckle upwards. Due to this failure the parapet wall is not significantly protecting the wall below from water entering.
Back to the top of page
Repairs
The type of repair work often depends on the extent of the damage and the cause. If the damage was the result of a misplaced movement joint, then at the location of new movement joints should be placed as discussed previously. If the extent of brick replacement is to be minimized then the movement joint should be located where significant cracks have formed. Prior to installing new joints, the lateral support of the proposed altered wall must be verified. Installing new joints can rapidly release stresses which might cause crushing, cracking, and instability of the masonry (Farmer 2010 pp 15-16).A lack of movement joints should not cause problems in older masonry with multiple wythes. The wall can better redistribute stresses from volume changes due to having more mass. The larger dead load also increases the shear resistance against horizontal movement. It is thus unwarranted and also difficult to install movement joints (Farmer 2010 pp 14).
Over the lifetime of a masonry wall it may experience net growth due to the effects of irreversible movement of the wall mentioned earlier. Thus joint widening can be anticipated as routine maintenance for some wall systems (Farmer 2010 pp 18).
The most common procedure for repairing the facade is replacement. It is sometimes better to replace entire sections of the wall system rather then just the damaged area. Whereas replacing just the damaged bricks can be tedious and challenging to patch up in an aesthetic way. Figure 19 shows a masonry arch wall that had to be entirely replaced including the steel lintel. If the flashing is missing or is improperly placed then large sections of the wall must be removed to allow for the installation of new materials.
Gorrell presents a case study of a 1960’s building 35’ tall, 220’ wide, and 540’ long which has a failure of its glazed brick veneer. Brick spalling was significant at the parapet wall and just below it. The parapet had a 12” cavity. The interior parapet wall is 6” concrete masonry backup with 4” brick. The exterior parapet wall is 4” concrete masonry backup with 4” brick (Gorrell 2007 pp 2). The coping did not provide a drip edge. A repair effort was made in the 1980's and some of the bricks were replaced. The movement joint was spaced about every 36’ and was stepped to follow the mortar joints of the bricks. The movement joints were not located near the corners of the building. The sealant used was over stretched and sealant was also used poorly to repair cracks (Gorrell 2007 pp 3). The flashing beneath the coping was missing. The flashing at the bottom of the parapet was cracked and did not typically extend to the outside. The wall ties were severely corroded. The roof had an irrigation system which inadvertently would spray on the parapet wall. This further increased the amount of water entering into the wall system (Gorrell 2007 pp 4). This shows an example of an unsatisfactory repair effort. The new restoration plan was then prepared and executed. The wall system was completely removed and rebuilt. The focus of the design was to prevent water infiltration, allow for quick drainage, and provide ventilation. Ties and bricks were also replaced for the wall below. The new design allowed for a 2” cavity between the facade and masonry backup to prevent blockages from mortar droppings (Gorrell 2007 pp 4). Glazed bricks shall be detailed to comply with ASTM C 1405 and BIA Technical Note 13 “Ceramic Glazed Brick Exterior Walls.” (Gorrell 2007 pp 9).
Back to the top of page
Conclusions
The first section covered the various components and variances that can be combined to create countless unique masonry walls. Many of the components are intended to prevent water from entering into the building. However, each one has failure modes which could then allow water or moisture in. These failure modes can often be classified as improper design, improper installation, or aging of the materials. A failure at one location may allow moisture in which may then cause damage such as spalling due to freeze / thaw cycles or metals rusting. This damage often leads to an increase in water infiltration as well as infiltration at new locations. Integrating the materials together is one of the most challenging aspects to a good design for a masonry wall to resist water entering the building. It is difficult to determine how well a wall will perform considering only the properties of the materials. Experimental testing is appropriate, since the interconnections are often the weak points.Restoration of a failed wall system is unique to each wall system. This makes this difficult to generalize an example for this discussion. and This is also difficult for the owner if a particular solution is the best solution for his interests. Thus, at least two alternatives for remediation should be presented to the owner including the benefits and drawbacks of each. One remediation solution sould represent the minimal amount of work that is required. This option will hopefully be economical, but does not provide the best protection against future issues. Consider a general case of a masonry cavity wall system that has cracks caused by a lack of or improper spacing of movement joints and additional damage caused to the bricks by water intrusion.
The first option would integrate new flashing, install movement joints, improve the drainage system, and replace bricks within a small range of where damage was noticed. The drawbacks to this option is that it may be more difficult to integrate the new flashing with the existing flashing at the edges of the scope of work. This could lead to water intrusion and resulting damages which lead to higher maintenance costs and/or another rehabilitation effort. Also, matching the color and texture of the new bricks with the old bricks may be difficult and become noticeable patchwork.
The other option should be the most complete and through. This option will most likely to have the highest initial cost, but it should offer the best protection against future issues and thus future expenses. For the same example, this option would require large sections of the wall to be replaced. This would allow for better craftsmanship and consistency of the new flashing, movement joints, and drainage. Due to the difficult in matching color and texture of bricks, this method would allow for any aesthetic differences to be better hidden. As needed, alternatives should be provided that are in between these two extremes to best fit the owners interests.
Envelope Failure Case Studies
Henderson Connecting Link Facade
Location at Penn State, University Park, PA (Photos by Author)Click here to view the report
North Hall Residence Facade
Location at Philadelphia, PA (Photos by Author)Click here to view the report
Back to the top of page
Bibliography
Colantonio, Antonio, and Garry Desroches. (2005). "Thermal patterns on solid masonry and cavity walls as result of positive and negative building pressures." Paper presented at Thermosense XXVII, March 29, 2005 - March 31, , http://dx.doi.org/10.1117/12.606000.
Moisture accumulates within wall assemblies from the moisture in air moving across a temperature gradient. This paper outlines the thermal patterns creased by positive and negative building pressures. These then provide the air flow patterns due to pressure, wind, and the stack effect.
Farmer, Matthew C., and Edward A. Gerns. (May 2010.) "Design and use of expansion joints in new and existing clay masonry wall systems." Journal of ASTM International 7 (5), http://dx.doi.org/10.1520/JAI102864.
This paper clarifies and expands on the standard guidelines for joint placement, size, and spacing. It suggests placement and detailing for atypical situations such as existing buildings, parapets, solid masonry wall systems, and window lintels. Common installation and maintenance problems are addressed.
Gorrell, Todd A., and Ian R. Chin. (2007). "Investigation and repair of glazed brick cladding: A case study." Journal of ASTM International 4 (1), http://dx.doi.org/10.1520/JAI100266.
Water typically enters in through joints even with a glazed brick cladding. However, the glazing then prevents the water from evaporation from the face of the wall. The freezing of trapped moisture then causes spalling. This paper discusses common failure modes, design/detailing recommendations, and a case study including the repair of a spalling wall.
Greenwald, Jeffrey H., and Thomas C. Young. (2008). "Evaluation of the effectiveness of clear water repellent coatings on partially grouted single-wythe concrete masonry walls." Paper presented at 11th Symposium on Masonry, June 13, 2006.
Evaluates clear water repellent coatings. Repellents have grown in number and their chemical composition has changed during recent years. 14 walls were constructed and tested in accordance with ASTM E 514. The walls were tested uncoated, coated, and coated then aged 1 year outside then tested.
Hens, Hugo S. L. C. (June 2006.) "The vapor diffusion resistance and air permeance of masonry and roofing systems." Building and Environment 41 (6): 745-55, http://dx.doi.org/10.1016/j.buildenv.2005.03.004.
Test to measure the vapor diffusion resistance of composite layers. Cavity walls diminish the risk of condensation and helps dry the cladding after rainfall.
Karkare, Milind V., and Craig T. Walloch. (July 1, 1996). "Capillary suction model for concrete masonry and its application to integral water-repellent masonry." Paper presented at Proceedings of the 1995 Symposium on Masonry: Esthetics, Engineering, and Economy, December 5, 1995.
Capillary suction is the main mechanism of water absorbing into a masonry wall. This article proposes a new test method to characterize the capillary suction properties of concrete masonry. water capillary suction data for concrete block and Type S portland cement-lime mortar is presented for varying amounts of integral water-repellent (IWR) admixtures.
Krogstad, Norbert V., Richard A. Weber, and Michael J. Huhtala. (April 1, 2010). "Detailing masonry veneer/steel stud backup systems at fenestration systems to avoid moisture problems." Journal of ASTM International 7 (4), http://dx.doi.org/10.1520/JAI102735.
Over 20 years of water leakage and condensation problems were mostly related to the interface between masonry veneer and fenestration systems. The problems occur with aggressive exposures against inqdeuaately designed or construction drainage and air seals. In many cases drainage systems is not properly installed; air barriers and vapor retarders are not sealed to fenestration systems. Anchors, lintels, support angles, and sill flashings are not thermally improved. Paper outlines detailing the interface. Fenestraction types include typical storefront or operable windows and curtain walls.
Procter, Don. "A Case for Hydraulic Mortar." Masonry Construction, April 2001, 16-22.
Discusses the differences between hydrulic lime mortars and hydrated lime mortars as well as applications for restoration work.
Selvarajah, S., and A. J. Johnston. (January 1, 1995). "Water permeation through cracked single skin masonry." Building and Environment 30 (1): 19-28,
http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V23-3YMFR4H-M-1&_cdi=5691&_user=209810&_pii=0360132394E0033N&_origin=search&_coverDate=01/31/1995&_sk=999699998&view=c&wchp=dGLzVlb-zSkzS&md5=d5f79f84f14a1b49d3b7fde8964c0e09&ie=/sdarticle.pdf
Water seepage rates are compared for varying influences such as various geometric and environmental parameters, including rainfall intensity, wind speed, crack width and crack orientation. 4 rainfall intensitites, 5 wind speeds, 3 crack widths, and horizontal/vertical crack orientations. Thresholds are idenfified for which increases in the environmental factor does not significantly increase the seepage.
Subasic, Christine A.. "Stainless Steel vs. Copper Flashing." Masonry Construction, April 2001, 30-38.
Discusses the importance of flashing in buildings. It covers the benefits and drawbacks of stainless steel, copper, and a few other options.
Thayer, R. D. (September 1947). "Moisture control in masonry maintenance". Sewage Works Journal 19 (5): 911-4.
Spalling and cracking of concrete and brick; efflorescence of brick and tile; staining of stone and disintegration of mortar joints; rusting of reinforcing rods due to penetration of moisture; surface types of waterproofing materials; penetrating type; resinous material and inorganic silicones
Additional Resources
ASTM E 514 “Standard Test Method for Water Penetration and Leakage Through Masonry.”
Barrett, Peter. (November 1983). "RAIN PENETRATION THROUGH MASONRY WALLS." Insulation Journal (Watford, England) 27 (11): 35,36, 38-39.
Covers the fundamental principals of water infiltration and the ineffectiveness of some cladding examples.
Beall, Christine. (June 1988). "CONTROLLING MOISTURE MOVEMENT IN MASONRY WALLS". Construction Specifier 41 (6): 36,42, 45, 47.
Recommendations for designing in humid climate. Discusses cavity walls, flashing, material selection, waterproofing, dampproofing, condensation, construction of vapor barriers, application of finishes, and controlling moisture movement.
Butt, Thomas K. (2006). "Water resistance and vapor permeance of weather resistive barriers." Paper presented at ASTM E06 Symposium 2004, April 18, 2004.
Weather-resistive barriers (WRBs) resist both water and air passage, but allow moisture movement. This article provides some light to the lack of comparable material properties and selection guilds. Both building code requirements and vendors' product information are inconsistent and confusing.
Conwell, Scott M. (January 1, 2005). "Water-resistant single-wythe masonry walls." Construction Specifier 58 (1): 63-6.
Proper detailing, attention to applicable code requirements, sensitive material selection, and gold workmanship are necessary for wall performance and water resistance.
Demars, Y., and Y. Buck. (1982). "WATER VAPOR DIFFUSION THROUGH INSULATED, MASONRY BUILDING WALLS." Paper presented at Moisture Migration in Buildings. .
Compares theoretical prediction and experimental results. Discusses conventional permeability values and conditions for condensation.
Farmer, Matthew C. (2005). "Traditional brick masonry detailing meets modern cavity wall construction - A difficult marriage." Paper presented at 2005 Structures Congress and the 2005 Forensic Engineering Symposium - Metropolis and Beyond, April 20, 2005 - April 24, 2005.
This paper attempts to identify some critical considerations when traditional aesthetics are applied to modern cavity wall construction. Through exploration of these challenges and their eventual solutions, it is hoped that designers will consider the constructability of desired masonry detailing to help avoid serviceability problems in the future.
Janopaul Jr., Peter. (1999). "Use of polyurethane foam to provide a watertight concrete masonry wall and a sealed connection of the wall to the foundation." ASTM Special Technical Publication(1352): 163-72.
The critical elements in perfecting this procedure are the detailing of the base of the wall, with a continuous exterior first course foam side cleanout, then following this detailing in the field construction of the wall, and properly foaming the constructed wall with polyurethane foam. The polyurethane foam must be poured into the foam cavity after the face shells have been replaced at the first course cleanout.
Krogstad, Norbert V., Richard A. Weber, and Dennis K. Johnson. (July 1996). "Common problems at the interface between masonry drainage walls and windows." Paper presented at Proceedings of the 1995 Symposium on Masonry: Esthetics, Engineering, and Economy, December 5, 1995.
Considers how deficiencies at windows can lead to water leakage, water staining, peeling paint, condensation, mold, and mildew. The windows considered include horizontal ribbon, shallow/deeply recessed punched windows, and vertical strip windows. Multi-component flashings are used to prevent thermal bridging, water, and air leakage.
McGinley, W. M., and Denis A. Brosnan. (July 1996). "Water penetration testing of single wythe residential load-bearing clay masonry wall systems." Paper presented at Proceedings of the 1995 Symposium on Masonry: Esthetics, Engineering, and Economy, December 5, 1995.
Summary of investigation including 18 wall specimens using ASTM E 514 Insulation, tie connectors, and moisture barriers were varied to create 6 different configurations. Construction procedures are discussed and recommendations are made for detailing.
O'Connor, T. F., and H. L. Droz. (July 1996). "Design considerations for sealants when used at horizontal expansion joints in masonry cavity walls." ASTM Special Technical Publication(1286): 63-83.
Inadequate considerations of flashing materials and sealant installation conditions let to poor protection against leaks. This paper suggests a tube and plate support design. Deflection, rotation, erection tolerances, and flashing materials are provided.
Olson, Eric K. (February 1, 2005) "Avoiding the perils of paper-faced exterior gypsum sheathing" Construction Specifier58 (2): 65-9.
The threats of mold growth on public health and wall systems are discussed. Varies factors of growth are mentioned. CMU walls are considered as any alternative to prevent mold growth.
Back to the top of page