A 20-foot chimney stack in Detroit taught me to never trust old mortar without a test patch

We were repointing a century-old factory chimney last spring and the original lime mortar just crumbled away like sand when we started. I had to stop the whole crew, mix a small test batch with a 3:1 sand to lime ratio, and let it cure for two days on a spare brick before we went any higher. Has anyone else had to completely halt a job to figure out the right mix for historic brickwork?

3 comments

3 Comments

jade2401mo ago

Had that happen on a brownstone last year. We ended up using a super soft 4:1 mix with hydrated lime and it bonded perfectly. Saved us from a total blowout.

kelly_henderson8319d ago

Yeah absolutely, that's the exact move we had to pull on a church restoration a couple years back. The original mortar was basically dust and we were sweating bullets thinking we'd have to tear out half the wall. Mixed up a real soft 4:1 with the lime putty instead of hydrated lime and just babied it into the joints. It grabbed hold like nothing else and now it's been solid through three winters straight. Sometimes you just gotta trust the old school recipes even when everyone else is telling you to go with something stronger. That soft mix saved our butts too.

ben1381mo ago

Interesting approach @jade240, but in my experience that mix can fail on older brick if the substrate isn't just right.