Tried repointing a 1920s chimney with Type N mortar and it crumbled within 6 months

I had a job last spring on a house in the Bronx, old brick chimney that needed repointing. I used Type N mortar like I always do for newer work, mixed it myself, did a clean job. By December half the joints were already flaking out and cracking. Turns out old soft bricks from that era need a lime-based mortar, not Portland cement. I had to chip it all out and redo it with a custom mix of lime putty and sand. That was a solid 40 hours of labor down the drain. Has anyone else ran into this with pre-war buildings?

2 comments

2 Comments

the_rowan1d ago

Oh man, that's rough. I had a similar learning experience with a 1910s storefront in Brooklyn. Used a standard Portland mix for the brickwork and the mortar ended up harder than the brick itself. Over the winter, the bricks started spalling, actually flaking apart from the inside out because the moisture couldn't escape. Had to rip out a whole three-foot section of wall and match the old sand-lime recipe by eye. Took three tries to get the color right, and the client still complained it looked too patchy. Nothing beats the sinking feeling of watching your own work fall apart in the cold.

lewis.mila1d ago

Ever accidentally built a brick that's harder than the actual stuff you're working with?