CCMA | Wall Movement

Cold Weather Construction
Masonry construction can continue during both hot and cold weather conditions. The ability to continue masonry construction in adverse weather conditions requires consideration of how environmental conditions may affect the quality of the finished masonry. In some cases, environmental conditions may warrant the use of special construction procedures to ensure that the masonry work is not adversely affected.

Cold Weather Construction
Materials selected for normal temperature construction will generally require little change during construction in low temperature weather other than insure that their temperature is conducive to hydration of the cement.

Mortar and Grout Performance
Hydration and strength development in mortar and grout generally occurs at temperatures above 40° F (4.4° C) and only when sufficient water is available. However, masonry construction may proceed when ambient temperatures are below freezing, provided the mortar or grout ingredients are heated and the temperature of the freshly constructed masonry is maintained above freezing during the initial hours after construction.

Effects of Freezing
The water content of mortar is a significant factor affecting mortar properties. When mortars with water contents in excess of 8% freeze, the resulting expansion has a disruptive effect on the cement-aggregate matrix of the mortar (ref. 1). This disruptive effect increases as the water content increases. Therefore, mortar should not be allowed to freeze until the mortar water content is reduced from the initial 11% to 16% range to a value below 6%. Dry concrete masonry units have a demonstrated capacity to achieve this moisture reduction in a relatively short time, commonly with
3 to 5 minutes (ref. 1).
Grout is a close relative of mortar in composition and performance characteristics. During cold weather, however, special attention must be directed toward the protection of grout because of the higher water content and resulting disruptive expansion that can occur from freezing of that water.
Like mortars, grouts undergo the hydration process, gain strength cool down, lose moisture to the adjacent masonry units, and require protection through material heating or enclosures. Unlike mortars, grouts are confined within the enclosed cells of hollow concrete masonry units. To maintain grout fluidity and mobility during placement, water content must be maintained at a very high level. These conditions make grouted masonry particularly vulnerable to detrimental expansion with early freezing. Therefore, grouted masonry needs to be protected for longer periods to allow the water content to be dissipated.

Ambient Temperature	Construction Requirements
25 to 40° F (-3.9 to 4.4° C) or masonry units below 40 F (4.4° C)	Do not lay masonry units having a temperature below 20° F (-6.7° C). Remove visible ice on masonry units before the unit is laid in the masonry. Heat mixing water or sand to produce mortar and grout temperatures between 40 and 120° F (4.4 and 48.9° C). Maintain mortar above freezing until placement.
20 to 25° F (-6.7 to -3.9° C)	Same as above, plus use heat sources on both sides of the masonry under construction and install wind breaks when wind velocity exceeds 15 mph (24.1 km/hr).
below 20° F (-6.7° C)	Same as above, plus provide an enclosure for the masonry under construction and use heat sources to maintain temperatures above 32° F (0° C) within the enclosure.

Mean daily temperature	Protection Requirements
32 to 40° F (0 to 4.4° C)	Protect completed masonry from rain or snow by covering with a weather-resistive membrane for 24 hours after construction.
25 to 32° F (-3.9 to 0° C)	Completely cover the completed masonry with a weather-resistive membrane for 24 hours after construction.
20 to 25°F (-6.7 to -3.9° C)	Completely cover the completed masonry with insulating blankets or equal protection for 24 hours after construction.
below 20° F (-6.7° C)	Maintain masonry temperature above 32° F (0°C) for 24 hours after construction by enclosure with supplementary heat, by electric heating blankets, by infrared heat lamps, or by other acceptable methods.

High temperatures, solar radiation, and ambient relative humidity influence the absorption characteristics of the masonry units and the setting time and drying rate for mortar. When mortar gets too hot, it may lose water so rapidly that the cement does not fully hydrate. Early surface drying of the mortar results in decreased bond strength and less durable mortar. Hot weather construction procedures involve keeping masonry materials as cool as possible and preventing excessive loss from the mortar. Specific hot weather requirements of the Specifications for Masonry Structures (ref. 3) are shown in Tables 2a and 2b.

Table 2a -Hot Weather Masonry Preparation and Construction Requirements (ref. 1,3)

Ambient temperature	Preparation and Construction requirements
Above 100° F (37.8°C) or above 90° F (32.2° C) with a wind > 8 mph (12.9 km/hr)	Maintain sand piles in a damp, loose condition. Maintain temperature of mortar and grout below120° F (48.9° C). Flush mixer, mortar transport container, and mortar boards with cool water before they come into contact with mortar ingredients or mortar. Maintain mortar consistency by retempering with cool water. Use mortar within 2 hours of initial mixing.
Above 115° F (46.1° C) or above 105° F (40.6° C) with a wind > 8mph (12.9 km/hr)	Same as above, plus materials and mixing equipment are to be shaded from direct sunlight. Use cool mixing water for mortar and grout. Ice is permitted in the mixing water as long as it is melted when added to the other mortar or grout materials.

Mean Daily temperature	Protection Requirements
Above 100° F (37.8° C) or above 90° F (32.2° C) with a wind > 8 mph (12.9 km/hr)	Fog spray all newly constructed masonry until damp, at least times a day until the masonry is three days old.