Masonry Magazine September 2004 Page. 22
Cold Weather
CONSTRUCTION
TABLE 2. COLD WEATHER PRACTICES FOR MASONRY UNDER CONSTRUCTION
When Ambient Temperature is:
32°F to 40°F (0°C to 4.4°C)
25°F to 32°F (-3.9°C to 0°C)
20°F to 25°F (-6.7°C to -3.9°C)
20°F (-6.7°C) and below
Mortar
Heat sand or water. In addition, heat sand AND water AND keep mortar above freezing until it is used. In addition, heat masonry surfaces under construction to 40°F (4.4°C) or higher and use wind breaks or enclosures when wind exceeds 15 mph (24 km/h). In addition, provide an enclosure and auxiliary heat to maintain air above 32°F (0°C) within enclosure. Heat materials ONLY if below 32°F (0°C)
Grout
In addition, heat grout aggregates or water to produce grout between 70°F and 120°F (21.1°C and 48.9°C). In addition, heat masonry to a minimum of 40°F (4.4°C) prior to grouting.
Source: Specification for Masonry Structures (ACT 530.1-02/ASCE 6-02/95TMS 602-02)
Accelerators are sometimes mistakenly called "antifreeze" admixtures. Their function is not to reduce the freezing point of mortar, but to increase the rates of early-age strength development. Thus, they don't eliminate the need to protect mortar from freezing, but may limit the amount of time that protection is required.
Keep in mind that while accelerators are helpful in cold weather, they do not eliminate the need for other cold weather construction practices. Be very careful: Unless project specifications call for the use of an accelerator, the mason must request permission from the specifier in order to use one. ASTM C1384 provides criteria for evaluating admixtures, including accelerators, for use in masonry mortars.
Calcium chloride - at a limit of 2% by mass of cement - is commonly used in concrete as an accelerator, but its use in mortar is prohibited by the Specification for Masonry Structures because it contributes to corrosion of embedded metal such as wall ties, anchors and joint reinforcement. Only non-chloride based accelerators, as verified by the admixture manufacturer to meet ASTM C1384, should be allowed.
The Engineered Wood Specialists! For Industrial Applications... Scaffold Plank • MasterPlank • TecLam • Microllam Concrete Forming Building & More! CAUSEY LUMBER CO. Roseville, Michigan 800.365.9663 Fax 586.294.1505 www.mccauseylumber.com CIRCLE 160 ON READER SERVICE CARD September 2004
Protection, Storage and Heating
ALL MASONRY MATERIALS should be protected from rain, snow and ice. Masonry units and packaged mortar materials should be securely wrapped with canvas or polyethylene tarpaulins and stored above the reach of moisture migrating from the ground. Sand piles should also be covered and care taken to avoid contamination of the sand with mud and clay.
The level of protection required will depend on the severity of weather encountered as defined by anticipated mean daily temperatures.
Masonry materials may need to be heated prior to use to assure cement hydration in mortar. At temperatures of less than 40°F (4.4°C), cement hydration necessary for strength development is minimal. At temperatures of 120°F (48.9°C) or higher, flash set is imminent. This means
www.masoncontractors.org