I'm writing this from my office (aka my basement). Summer’s over and there’s a little nip in the air…
Studio Audience: How cold is it?
Me: It's colder than a polar bear's toenails! I'm saying it's cold!
Studio Audience: HAHAHA! How cold is it?
Me: It's so cold, I chipped my tooth eating soup! I'm saying it's COLD!
Studio Audience: HAHAHA! How cold is it?
Me: It's so cold...I tried to build a masonry wall and my mortar wasn't able to gain sufficient strengths before the expansive action of water freezing damaged it irreparably!
Studio Audience: Haha ...Wait....wha?
If construction stopped every time it got below 40 degrees in Western PA, nothing would get built. We're a masonry market here through and through. But what can be done when temperatures drop below the acceptable range for installation?
Heat Your Materials - Between 40 and 32 degrees, the International Masonry Institute recommends heating at least one of your mortar components (typically either sand or the water). The warmer mixing temperatures allows the cementitious component of your mortar to do its thing.
Tent It In - Once you get below 25 degrees, the IMI recommends tenting in the area and pump heat into it, bringing the temperatures to an acceptable level. This is good for your masonry and your masons!
Use an Admixture - Using an accelerating admixture like Euclid's Accelguard 80 kickstarts the chemical reaction between the water and cementitious material. This accelerated reaction offsets the delay caused by temperature, allowing the mortar to gain strength rapidly and fight off Jack Frost.
If you want a really quick primer, here's my man Bob Villa on a classic episode of This Old House talking about cold-weather masonry.