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Hot Weather Masonry

By Jeff S. Barnes

Summer is upon us and thoughts have turned to sunny days at the beach, driving around with the windows down and the music up, vacations, and the 4th of July.  The summer also brings heat, humidity, and unexpected thunderstorms.

By June/July the construction season is in full swing.  As building owners rush to get their projects completed before fall, the unanticipated New England weather can really impact the construction schedule.  During this time of year, most contractors don’t concern themselves with weather because, generally, the temperature is ideal for construction.  That being said, contractors, and especially masons and waterproofers, need to pay attention to summer conditions as the weather can change quickly from morning to afternoon.

In the morning, before the sun has fully reached its highest point, the side of the building (elevation) being worked on can be partially covered in shade with the temperature just right for masonry work (70°F, 50% relative humidity, with no forecast of rain).  As morning turns into afternoon, the humidity climbs and the sun is now blazing on the same elevation that was just pointed, baking the building surface.  The sun beating down on the new masonry work is quickly evaporating the water from the mortar, creating shrinkage cracks. 

Many contractors don’t have protection provisions on site during the summer months, such as tarps or burlap blankets and the labor to hang or install them, or to protect the new work.  If your contractor isn’t carrying protection or protecting the new work, they most likely aren’t prepared to cure the masonry work either.

Shrinkage cracks in new pointing after not being protected and cured properly during summer construction.

The Brick Industry Association defines hot weather as ambient temperature above 100°F.  If the surface of the building being worked on is 100 degrees or above it also falls under “hot weather conditions”.

Protecting the masonry materials in hot weather conditions is very important.  Those materials typically consist of masonry units (brick, CMU), mortar, sand, and cool water.  All materials should be kept in the shade and away from direct sunlight before use.  The mortar used should be kept at less than 120°F but it can be re-tempered with cool water to maintain consistency during “hot weather conditions”.  Sand should be kept in a loose, damp condition by sprinkling it with water and leaving it uncovered.

Protecting the completed masonry work typically consists of wet curing or spraying the new work three times a day for three days when:

  • the average daily temperature exceeds 100 degrees
  • is 90 degrees with a wind speed over 8mph
  • or the surface of the new work is 100 degrees or higher.

These protections, once put in place, should prevent rapid loss of moisture from the new masonry work.  Combined with proper masonry techniques, it should result in a building that will last for years to come.