Hot & Cold Weather Masonry Construction

Performance of Units

General. While considering the influence of the masonry unit on the performance of cold weather masonry, one should distinguish between units laid cold and units that are preheated.

A cold masonry unit will exhibit performance characteristics of a heated unit, except that the volume of the unit is, or may be, the smallest it will ever be within the masonry. If the cold masonry unit is wet and frozen, the absorption characteristics may be decreased due to ice blockages in the pores and channels of the unit.

Preheated masonry units exhibit performance characteristics of units used during normal construction, except the heated unit may withdraw more water from the mortar because of the absorptive characteristics of a cooling body.

Basis of Selection. An absorptive masonry unit will withdraw water from the masonry mortar and lessen the possible disruptive expansions that may occur in the mortar on first freezing. Conversely, a very low absorption unit will not draw sufficient water to prevent mortar and masonry expansion. Auxiliary dry heat to promote mortar strength and drying may be required for very low absorptive units such as glass blocks.

Temperature Effect. The temperature of the masonry unit and the ratio of its volume and density to those of the mortar joint are further contributors to the freezing rate of masonry. Excessively cold masonry units, even when dry, may rapidly withdraw heat from the mortar and increase the rate of freezing.

Summary. Below-normal temperatures may affect the performance of masonry units, even when dry. Wet units may freeze before use and alter the freezing characteristics of the mortar. If used, wet, frozen units need to be thawed, being careful not to over-heat the unit.

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