Debate: Silicone sealant vs traditional mortar for repointing old chimneys?

I had to pick between using a high-end silicone sealant or sticking with traditional lime mortar for a 1920s chimney job last week. The silicone was $45 a tube and claimed to flex with movement, but the old-timer I work with swore the lime mortar breathes better and won't trap moisture. I went with the silicone since the homeowner wanted a 10-year guarantee, and it went on easy enough. But I'm worried I might've sealed in damp that'll crack the bricks later. Has anyone here tried both on historic stuff? What's your experience been with moisture getting trapped?

3 comments

3 Comments

grace_knight7027d ago

Big time. Did a 1930s house last year with silicone on the advice of the supply house guy and the bricks started spalling within like 8 months. Had to tear it all out and go back with lime mortar. That moisture trapping is no joke, especially on older brick that's softer. You might be lucky if that chimney gets lots of sun and dries out fast, but I'd keep an eye on it.

drew69027d ago

Man, that's rough. I had a buddy who sealed his 1920s foundation with the wrong stuff and ended up with damp rot in the sill plates within a season. You'd think @grace_knight70 would agree, that old brick just needs to breathe.

elliotadams27d ago

Lime mortar actually cures harder than silicone over time and lets the wall dry out, while silicone can trap moisture like a plastic bag. Might want to check on that chimney after a few good rainstorms to catch any issues early.