Hot Weather Masonry-Mortar and Grout Performance

General. During hot weather masonry construction, the mortar’s temperature and properties, the masonry unit’s temperature and properties, wind velocity, and relative humidity influence the rate at which mortar sets. As the temperature of the mortar increases, the following physical property changes take place:

a. Workability is reduced, or the addition of more water is required to maintain a given workability

b. Initial and final set occur earlier

c. Depending on the surface characteristics, temperature, and moisture content of the masonry units, moisture loss from the mortar due to suction takes place much more rapidly

d. A given amount of air-entraining agent yields less entrained air

Rapid water loss due to evaporation and suction reduces the amount of water available for hydration of the cement. Since hydration of cement is necessary for normal strength development of mortar, a reduction of strength development may occur under rapid drying conditions. Evaporation removes moisture more rapidly from the surface of mortar joints resulting in weaker mortar on the surface. Covering the walls immediately after construction will effectively slow the rate of water loss from the masonry, while the application of a fog spray during the first 72 hours can reduce the effects of hot, dry, windy weather. Strength development in masonry subjected to early dry-out often can be reactivated by spraying the masonry with water. Grout will also be susceptible to a rapid set at above normal temperatures. The effects are primarily influenced by the temperature of the wall into which the grout is placed. This will influence placement procedures, not final strength.

Summary. Mortar temperatures and properties, masonry unit temperatures and properties, wind velocity and relative humidity can affect the performance of mortar. Cooling mortar materials, covering the wall immediately after construction, and the application of a fog spray to the surface of the wall in hot weather can provide needed workability in the plastic mortar and the necessary water required to provide proper strength development.

Resource: Masonry Institute of St. Louis – www.masonrystl.org

Hot & Cold Weather Masonry-Publication of Masonry Industry Council