Cold weather curing can be a challenge because the curing process slows down. As the temperature drops, curing slows. Moist air, fog, rain, winter weather can turn a 48 hour scratch coat cure or a 7 day brown coat cure into a 10 day cure. The requirements to moist cure become less stringent during the winter so a specifier or contractor needs to be aware and not over wet the walls and create other issues.

Curing Plaster is what gives the product it’s performance characteristic hardness. A simple way to confirm the cure is the Moh’s Hardness test. Moh’s has given numbers to a set of products from Talc at 1 to Diamond at 10. Plaster should be harder than a penny which is a 5 on the scale. So scratching a penny across a scratch coat or brown coat with the wall scratching the penny confirms a cured wall.

In working with a contractor during winter plaster installations, an architect’s specification to moist cure morning and evening might not be the wisest choice. Drying is equally as important to the process of curing as moisture added back into the plaster panel. Having the scratch test in your back pocket to confirm what’s going on with your walls is a must.

One needs to let the plaster set before applying moisture. A fine spray of moisture starting at the top of the wall until you can see the water coming from the weep screed at the base of the wall saturating the whole wall works best.

If you have questions about this condition or other situations, call or email:

Bruce Bell
Bell Construction Consulting

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