FAILURES
David Patterson, AIA and Deborah Slaton
Planning for weather, despite its unpredictability, is an important part of scheduling construction activities. Certain building materials can only be applied during specific temperature and humidity/moisture conditions.
Masonry installation, pointing, and repair are subject to potential failure when installed in temperatures too cold or hot. Placement of mortar and grout is more difficult in cold weather. Mortar that freezes during installation or curing prematurely fails, while mortar installed during excessive heat may exhibit extensive cracking.
The Brick Industry Association (BIA) provides guidance on both hot and cold weather masonry work in its Technical Note No. 1. The publication defines ‘cold’ as 4.4 C (40 F) and below, and ‘hot’ as above 37.8 C (100 F). Depending on the range of temperatures, BIA recommends cold-weather procedures that include:
- heating materials (within specified limits);
- removing frost, ice, and snow from surfaces; and
- covering or enclosing the masonry during and after the work (with use of supplemental heat as necessary).
Admixtures are sometimes used with mortar and grout to accelerate setting time in cold weather but must be used with caution; some accelerators contain chlorides that cause corrosion of embedded metals.
BIA’s various recommended hot-weather procedures include:
- dampening materials before use;
- using cool water for mortar mixing; and
- providing shade and protection from wind.
Sealant installation is also weather-dependent. Although some sealants can be installed at temperatures as low as –29 C (–20 F), most sealants should not be installed at temperatures below 4.4 C or above 26.7 C (80 F), or before or after rain or snowfall. Solvent-based sealants can be applied in cold temperatures, although flow rates are affected, and curing is typically slower because the solvent’s evaporation rate is reduced. Moisture-cure sealants also cure more slowly at colder temperatures and lower humidity.
Temperatures at or below freezing can cause ice or frost to form on bonding surfaces, affecting cure, adhesion, and long-term performance. Application of sealants in excessively hot weather can result in blistering of the sealant.
Many coatings are sensitive to ambient and substrate temperature and moisture conditions; manufacturer’s product literature should be consulted for the allowable range of temperatures. Other construction materials and processes (e.g. concrete placement, membrane applications, façade-cleaning) are also subject to temperature limitations. Even for materials and construction activities less sensitive to weather (e.g. some types of roofing work), careful consideration should be given to temperatures, precipitation, wind, and other environmental factors affecting installation and performance.
Specifications should note recommended temperature ranges and other environmental constraints on material use, and should recognize some building codes include cold- and hot-weather construction provisions. During the work, environmental conditions need to be monitored daily (sometimes, hourly).
The BIA technical note makes an interesting distinction—it comments designers primarily review climatological data, while contractors are typically concerned with meteorological conditions during construction. Information concerning both types is available on the U.S. Department of Commerce’s National Oceanographic and Atmospheric Administration (NOAA) website—www.noaa.gov.
Of course, one should not forget climate conditions also affect workers, who might need special protection and may also have difficulty properly executing demanding tasks during extreme weather.
David S. Patterson, AIA, is an architect and senior principal with the Princeton, New Jersey, office of WJE, specializing in investigation and repair of the building envelope. He can be contacted at dpatterson@wje.com.
Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at dslaton@wje.com.
