Take good care of building facades; Watch for these six maintenance issues to preserve the exterior of your facility.
Brick is a very common type of exterior masonry; other masonry claddings include stone, terra cotta, and concrete masonry units (CMUs). All of these claddings have their differences, but each one experiences similar problems.
When mortar joints are hit by wind and moisture, they start to disintegrate. Loose mortar is washed away, and the mortar continues to wear. Eventually, the masonry units being held into place become loose and fall out.
Tuckpointing is a common maintenance repair for masonry walls. It involves filling in eroded/weathered mortar joints between masonry units with new mortar material. Prior to tuck pointing, the existing mortar joints should be properly ground (routed) to provide a clean substrate for the new mortar to adhere to.
Tuckpointing is often necessary to restore the integrity of the mortar due to normal weathering and aging of a masonry building; however, the need for tuckpointing often indicates more significant problems, such as a movement or shift in the vertical or horizontal plane of the wall.
Exterior masonry walls are especially susceptible to forces that cause cracking, including temperature, the introduction of moisture (resulting in volumetric changes of the materials), and corrosion of embedded steel elements. Each of these forces causes masonry to move. If the movement is too large, or if that movement is restrained, the masonry is prone to crack. Vertical expansion joints and horizontal shelf angles are generally installed to relieve the stresses caused by these forces in large expanses of masonry; however, these items aren't always properly installed, may require repair, or may not be present at all. Common repairs include removal and replacement of failed joint sealants, installation of expansion joints (where none previously existed), and tuckpointing of cracked mortar joints.
Cracks also occur in masonry walls due to settlement of the building's foundation. Differential settlement can cause one portion of the wall to move downward while the other portion remains in place. This non-uniform movement creates tension in the masonry and eventual cracking at weak points in the wall (typically the mortar joints). Eliminating future building settlement is a challenge. If a building's masonry exhibits signs of foundation settlement, evaluation of the potential for further settlement should be performed. Typically, a subsurface investigation, such as soil borings and geotechnical evaluations, are necessary--along with an engineering assessment--to determine the likelihood of further settlement.
It's important to identify cracks in their early stages in order to diagnose any underlying problems. The cracks should be evaluated by a qualified professional to determine the cause and the type of repair(s) necessary.
Spalling is a term used to describe portions of masonry that fall--or that are ready to fall--off a structure. Spalls can range in size from 1 square inch to several square feet (or bigger). Masonry that exhibits signs of spalling presents a potentially risky situation for people, property, and building owners/managers, When masonry falls from a building, it can cause bodily harm and/or significant damage to property below.
Some cities have enacted ordinances that require high-rise buildings to have periodic facade inspections. The intent of these inspections is to discover any potentially hazardous conditions and mitigate them before they become inherent risks to people in the vicinity of the building and the surrounding property. During these inspections, dangerous spalls will often be removed to prevent future problems.
Spalls may be present for a variety of reasons. Moisture infiltration into the wall and corrosion of metal within the wall are common causes of spalls. Masonry materials are porous and will absorb water--if a saturated masonry unit is exposed to below-freezing temperatures, it will cause the water molecules inside the unit to freeze and expand, causing a portion of the unit to spall. Similarly, when steel elements corrode, they expand; this expansion creates a force on the masonry, resulting in a spall
Efflorescence is the presence of salt residue leeching from within the masonry material that forms on the exterior surface of the wall. It's generally caused when a large amount of water within the wall filters out through the face of the wall. Efflorescence may be unsightly, but it's not typically indicative of a structural problem; however, the presence of residue is a symptom of a potential problem. This excessive moisture may cause weakening of the mortar joints and may eventually deteriorate the masonry units.
It's difficult to stop water infiltration until the actual source is identified, so it's important to understand the root cause of efflorescence. A common method of tracing sources of water infiltration involves water testing, along with a review of original building drawings and targeted inspection openings. Once the source(s) of water infiltration is determined, a plan for the design of the wall repairs can begin. Repairs can range from tuckpointing to installation of a properly designed through-wall flashing system. In severe cases, it may be necessary to reconstruct a portion of the distressed area.
Lintels support the masonry over openings in a wall, such as at doors or windows. Lintels are generally constructed of steel angles, channels, wide flange beams, or reinforced masonry bond beams. Steel lintels are susceptible to corrosion through repeated cyclical exposure to moisture. The corroded steel can expand by up to 10 times its thickness. This corrosion and expansion of the steel exerts tremendous force on the adjacent masonry, which causes movement and eventual cracking in the wall.
Corroded lintels should be reviewed by a qualified individual. This may include the selective removal of adjacent masonry by an experienced masonry restoration contractor to facilitate a visual inspection of the steel. The extent of repair can vary directly based on the extent of the corrosion. Lintels that exhibit minor corrosion may need to be cleaned and epoxy painted. It's important that all corrosion is removed--typically via sandblasting--prior to the application of an epoxy coating. Severely corroded lintels may require complete removal and replacement with new galvanized steel members. A qualified professional should asses the severity of the corrosion and design the necessary repairs. Upon completion of the repairs or replacement of the lintels, the masonry contractor could then restore the masonry wall.
Parapets are the portion of exterior walls that extend above the roof level. Parapets are exposed to the weather on both faces and, thus, are often prone to accelerated weathering and deterioration. It's not uncommon to see parapets that are not properly secured to the roof structure and have deflected out of plane. Parapets that lean toward or away from the building should be evaluated in detail. Without proper maintenance and necessary repairs, severely distressed parapets could eventually collapse. Depending upon the severity of the deterioration, repairs of parapets can range from tuck pointing of the mortar joints to providing additional back bracing to the roof structure. In the most severe cases, it may be necessary to completely rebuild the parapet wall with steel reinforcing bars dowelled into the structure below the roof line.
These six items are some of the most prominent topics concerning exterior masonry wall maintenance. Different wall materials will exhibit different signs of distress; however, regardless of the material of the exterior wall construction, periodic evaluations and an ongoing maintenance program will significantly improve the aesthetics of your building and maximize the longevity of your building facade.
Michael F. Wiscons is the exterior wall department supervisor at Inspec Inc. (www.inspec.com), an engineering/architectural firm with offices in Chicago, Milwaukee, and Minneapolis.
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|Comment:||Take good care of building facades; Watch for these six maintenance issues to preserve the exterior of your facility.|
|Author:||Wiscons, Michael F.|
|Date:||Feb 1, 2010|
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