Tried a refractory mortar mix instead of my usual Portland cement for a chimney rebuild last month

Had this old chimney in a house near downtown Dayton that needed repointing after some freeze damage. I went with a refractory mix from a local supplier over my standard Portland stuff because the boss swore it handles heat expansion better. So far the joints are holding tight without any hairline cracks, but I'm still watching it through the winter to see if I made the right call. Anyone else used refractory in a residential stack and regretted it down the line?

2 comments

2 Comments

josephmartin11d ago

Oh man, I gotta say you might be overthinking this whole thing. I've seen refractory mortar actually cause more problems in residential flues because it's so rigid it can transfer stress to the brick itself instead of flexing like Portland does. Had a buddy in Cincinnati who used it in an 1880s chimney and the bricks started spalling along the mortar lines after two winters, completely trashed the whole stack. Not saying yours will do that, but I wouldn't relax until you've seen it survive a few hard freeze-thaw cycles, especially with that older clay flue liner.

taylor.hayden9d ago

Heard an old mason say the same thing about refractory mortar being too stiff for old brick, @josephmartin, and he swore by a lime-based mix for anything pre-1900. That Cincinnati story is a brutal reminder that modern materials don't always play nice with vintage stacks.