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Why does nobody talk about the difference between a 3/8 and a 1/2 inch mortar joint on a chimney?
I built two identical chimneys for a client in Boise, one with each size, and the 3/8 joint cracked within a year while the 1/2 inch is still solid. What's your go-to joint size for freeze-thaw areas?
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evanh275mo ago
Your point about the 3/8 joint cracking is really telling. I always used the smaller joint thinking it was stronger, but your real world test changes my mind. For freeze thaw cycles, I'm going with the half inch from now on.
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lisa6715mo ago
Yeah, the "real world test" part is key. I read a whole thing from a mason in Minnesota, @evanh27, where he tracked repairs over ten winters. Every 3/8 joint on a north-facing wall failed. The half-inch joints held, even with cheaper bricks. It wasn't about strength, but letting the material move. That small extra space makes all the difference when the water inside expands.
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emma3493mo ago
Nah, @lisa671, bigger gaps just mean more mortar exposed to the weather in my experience.
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