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A chat with an old timer in St. Louis flipped my view on lime mortar
I was helping this guy, Frank, repoint his 1920s chimney and he wouldn't let me touch his pre-mixed bag. He said, 'Kid, that stuff's too hard for these old bricks, you'll crack them in five years.' He made me mix my own with 3 parts sand to 1 part lime. Seeing how soft and breathable it was totally changed my mind on using modern cement for every job. Anyone else run into this on historic work?
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stella6277mo ago
See, I've had the opposite experience on some jobs. I get the breathability thing, but that soft lime mix can fail pretty quick on a chimney crown or below grade, especially with our freeze-thaw cycles. I've seen a lot of repointing from the 90s that used that exact 3:1 mix and it's already crumbling out. Sometimes a modified, weaker mortar mix is the better call for the long haul.
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kimlee7mo ago
Hold up, you're blaming the mix when it's probably the application. That 90s repointing job likely had zero prep, they just slopped it in there. A proper lime mix needs to cure slow, and nobody back then had the patience. A weak modern mortar just masks the real problem, which is water getting in behind it. Then you get spalling, and the brick itself fails, not just the joint. Going softer than the original material is a band-aid fix that causes bigger issues down the line.
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karen2756mo ago
Used to think softer was always better for old brick. Then I saw a whole wall spall apart because the weak mix trapped moisture. Now I'm way more careful about matching the original strength.
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