Update: I stopped using rapid-set mortar for residential work

I used to swear by rapid-set mortar for all my chimney caps and repairs. But after a job in Tulsa last summer, I noticed the mortar on a south facing wall was cracking within 3 months. Switched back to Type N with a slow cure and the same wall looks perfect a year later. Has anyone else seen rapid-set fail on hot exposures?

3 comments

3 Comments

jesser791mo ago

Whoa, that's wild. I once had a bag of mix that was all clumpy and just fell apart.

kai_park1mo ago

Ngl that sounds more like a mixing or curing issue than a product flaw. Rapid set works fine on hot exposures if you keep it damp during the cure.

kai_butler831mo ago

Used to be on team rapid-set myself. Hard sell to wait on a chimney cap when you can be done in 20 minutes. Then I had one fail on a west-facing parapet wall in August. Cracks showed up in under two months. Swapped to Type N and it's still solid two summers later. The heat soak is just too much for that quick cure chemistry. Damp curing helps but not enough for direct sun all day.