Exterior Brick Masonry Walls

I S S U E3/ 2 0 0 3 V O L U M E21 N U M B E R3Journal of architecturaltechnology publishedby Hoffmann Architects,specialists in the rehabilitationof building exteriors.Exterior Brick MasonryWalls:Causes of and Solutions to Inevitable DeteriorationScott D. ChamberlainThe history of brick, man’s oldestmanufactured building product, is long andstoried. Used in construction forthousands of years, it reflects the evolutionand variety of our ever-changingconstructed world.The first bricks were made from the mudof riverbanks and baked in the sun, aslong ago as 10,000 B.C. Chopped strawand grass were added to preventdistortion and cracking. Around 4,000B.C., brick manufacturers began producinguniform shapes and firing them in kilns.Firing caused the clay particles to bondchemically, hence improving brick’sdurability. The landmarked Chrysler Building in NewYork City is clad in glazed brick. Though thetowering structure is perhaps best known for itsshining spire, its facade features intricate,automobile-inspired brick patterns.Brick’s aesthetic appeal and diversity isundeniable. From the historic redschoolhouses that dot the countryside tothe landmarked Chrysler Building clad inglazed brick, from Thomas Jefferson’sMonticello to the low-rise buildings ofcontemporary suburban office parks, brickis represented in an astounding array ofarchitectural styles.Aside from its visual appeal, brick hasgreat longevity. It withstands the tests oftime and Mother Nature. Take, forexample,The Great Wall of China. Itsconstruction began in 221 B.C., and it stillstands strong today, even where it leans atangles as drastic as 70 degrees, acrosssome of China’s most severe andmountainous terrain.As with all building envelope systems,deterioration is inevitable. The key tosustaining brick masonry exterior wallsfor as long as possible is preventativemaintenance and repair. Preventingminor deterioration from escalating intobigger problems will ensure astructure’s longevity.Form and FunctionBrick masonry walls consist of uniformlyshaped and sized bricks that are laid incourses with mortar joints. A singularvertical section of brick masonry, oneunit in thickness, is referred to as awythe. Bricks can be of various colorsand hardnesses. They may be glazed,pressed or molded, or customized tosuit the design requirements for aparticular structure.Bricks need to conform to a number ofcriteria in order to be effective buildingblocks. They should be durable andmeet the required minimumcompressive strength dictated by thedesign. They should not exceedmaximum water absorption andsaturation guidelines, should pass(continued on page 2)Scott D. Chamberlain, Project Manager, oversees a variety of building envelope rehabilitation projects,including those for brick masonry facades, for Hoffmann Architects.

J O U R N A LFigure 1 Types of Brick Masonry ntinued from page 1)freezing and thawing tests, and shouldmeet the weathering challenges of aregion.For example, a brick specified for astructure in hot, dry southwestern NewMexico would likely fail in New Englandand other northern climates wherebuildings are subjected to a wide range ofclimatic conditions, including freeze-thawcycling.Waterproofing for Brick MasonryExterior WallsThe primary role of the buildingenvelope is to separate and protect aninterior space created by man from thenatural environment. First andforemost, it holds the forces of MotherNature at bay by sealing a buildingfrom the elements: wind, rain, snow, ice,thermal conditions (heat/cold).Water is a constant threat to thebuilding envelope’s ability to protectinterior space; it is a principle cause ofdeterioration in building envelopesystems, and it is no different in brickmasonry exterior walls. It is thereforecritical that, in addition to therequirements of structural design, anexterior brick masonry wall bedesigned to resist water infiltration tothe highest degree possible.Successful waterproofing of exteriorbrick masonry walls relies upon a clear2Reinforcedbrick masonrbrickmasonryy(barrier)understanding of the means by whichwater infiltrates a wall system; theproper construction of a selected wallsystem and its suitability for astructure’s particular climate; theappropriate use of various types ofspecified materials, such as brick andmortar; and, methods for expellingmoisture that has entered a wall, bymeans of flashing and weep systems.Types of wall constructionconstructionIn terms of waterproofing, exteriorbrick masonry walls can be classifiedas either barrier or drainage walls.Barrier wallsMore common prior to thedevelopment of cavity walls, barrierwalls are constructed of solid masonrywithout the use of a drainage cavity.They may be constructed of multiplewythes of brick, or they may becomposite walls constructed of brickmasonry combined with a variety ofmasonry materials such as ConcreteMasonry Units (CMUs) or terra cottablock. Barrier walls may also be loadbearing walls reinforced with steel tosupport or help support a structure.Single wythe barrier walls are generallyconstructed from a masonry unit thatis wider (deeper) than a standard unitmaking the wall more impervious towater penetration. However, singlewythe barrier walls are often not asCompositeCMU and brick(barrier)Cavity(drainage)successful at preventing waterinfiltration as drainage or multiple wythebarrier walls.Multiple wythe brick barrier walls thatare three wythes or more are designedto prevent water infiltration throughmass. While not always successful, theamount of water that the wall isallowed to absorb over a period oftime should be less than can bedissipated in the same period, keepingwater from reaching the interior surfaceof the wall.Narrower multiple wythe barrier wallsand composite walls depend on acollar joint to provide a barrier withinthe wall. The collar joint, grouted solidwith mortar, is the joint between theexterior wythe of masonry and thebackup masonry. The collar joint blockswater that penetrates the face of awall. That water then either follows thecollar joint down to the flashing levelwhere it is expelled through the bedjoint and/or weep holes, or it dissipatesout through the face of the wall.Drainage wallsDrainage walls are designed with acavity within the wall. The cavity islocated between the outer wythe ofbrick masonry and the back-upmaterial that may consist of brick,CMUs, metal or wood stud framing.

VOLUMELike the collar joint in a barrier wall,the cavity is designed to stop thepenetration of water that enters theface of a wall from traveling to theinterior, backup portion of a wall.However, instead of forming aphysical barrier, the cavity forms abreak that water has difficultycrossing. When water penetrates theface brick, it runs down the interiorsurface of the exterior wythe of brickto the flashing level where it isexpelled through the bed joint and/orweep holes.Furthermore, the cavity must be keptclean and free of debris both duringand after construction, as mortardroppings and other constructiondebris in the cavity may clog weepholes. Mortar, debris, and improperlydesigned brick ties may also bridgethe cavity, allowing water to penetratethe backup above the level of thewaterproofing.The symptoms of deterioration inbrick masonry wall construction areNUMBER3The Roles of Relieving (Shelf) Angles and Soft JointsBuilding components expand andcontract with changes in temperatureand moisture content. Relieving (orshelf) angles are necessary toaccommodate this movement inmasonry walls. If a relieving angle isomitted, cracks will develop where thebrick is restrained as the brick grows andthe backup shrinks.Soft joints should be constructed atrelieving angles to create relief forbrick’s expansion. If soft joints atrelieving angles are not properlyconstructed, the brick will be crushedand water will be allowed into the wallsystem. Control and expansion jointsare needed vertically as well. Withoutexpansion control, brick will slide off ofthe relieving angle.What happens when relievingangles are omitted? Cracking. Here,brick has expanded; the backup hasshrunk; and, cracks have developedwhere the brick is restrained atbalconies, windows and vents.generally easily detected by visualinspection. Symptoms include:· staining and efflorescence;· cracking;· spalling;· deteriorated mortar joints;· loose, displaced or crushed brick;· mildew, a fungus; and,(continued on page 4)These mortar joints appear to be properlytooled, yet there is a lack of adhesion between themortar and the brick. The cause? Either the mortarhad begun to set too early or the brick was verydry at the time of repointing. A repointing project isonly as good as its weakest component. Symptoms and Causes ofDeterioration in Brick Masonry WallConstruction In order for drainage walls to beeffective, careful consideration mustbe given to design details forflashings prior to construction.Improperly installed flashings will fail.21 Below left, cracking through brick masonry wall. Below middle, eroded mortar joints below this cornice . Below right, inadequate partial repointing has left manymortar joints vulnerable to water intrusion.3

J O U R N A L(continued from page 3)· vegetative growth, such as moss inmortar joints.The usual suspects: failed orinadequate flashing and weep systemsMortar deteriorationMortardeterioriorationA key component in both drainage andbarrier wall systems, flashing is animpermeable membrane that forms ahorizontal barrier that stops the verticalmovement of water and directs it out ofa wall system.Mortar is as integral to brick masonrywall construction as bricks themselves.Mortar holds a masonry wall togetherand serves as a barrier against thepassage of air and water. Somecommon causes of mortardeterioration include improperly tooledjoints; water infiltration that washesaway mortar’s soluble salts, reducing itsimpermeability; and, the eroding forceof wind and rain.Loss of mortar leaves an exterior wallvulnerable to water infiltration.Repointing is required when the bondbetween the mortar and the brick isbroken, when mortar has crumbledfrom the joint, when hairline cracksappear in the mortar, and whenmortar has eroded to expose theback-up wall material.EfflorescenceEfflorescence occurs when waterwashes soluble salts out of mortar andonto the surface of brick. White stainsand/or build-up of white, crystallinestructures develop on brick surfaces asthe water evaporates.Cracking and spallingExpansion from thermal changes, fromwater absorption and from freezingand thawing of retained moisturecauses cracking and spalling (thebreaking off of the face of brick) inbrick masonry walls. The corrosion ofembedded steel reinforcing in masonrywalls may also lead to cracking andspalling of brick.4Weep holes provide a direct route forwater to exit a wall. In order to beeffective, weep holes should be locateddirectly above all areas of flashing.Installing weeps too far above flashingis a mistake, as water may collectbeneath the weeps and back up at theflashing.A flashing and weep system is anintegral part of an exterior brick masonrywall system and key to expelling waterfrom within a wall. However, unlessproperly installed and maintained,flashing and weeps can be a cause ofwater infiltration and damage to a wall.When Flashing and Weep Systems Fail.Counter-clockwise from left:Leaks in the flashing at this windowlead not only to water infiltration intothe building, but also to corrosion ofsteel lintels and deterioration of theanchorage system that supports thebrick face.Efflorescence at brick masonryunder cornices and belt courses is asure sign of water infiltration throughleaking flashing or open butt joints in thestones above.The bed joints above the throughwall flashing at the base of this wall havebeen sealed over, trapping moisturewithin the wall, causing spalling of brick.The bed joints above the throughwall flashing have been sealed over atthis roof parapet, causing waterretention. Note moss growth andefflorescence.