Found out modern lime mortar can actually damage old brick faster than cement... where's the line?

I read this article from a conservation group in Boston claiming that using any Portland cement on pre-1900 brick traps moisture and makes the face of the brick pop off in 5-10 years. On the other hand, my grandpa has been patching his 1920s house with type N mortar for 30 years and it's still standing - so who's actually right about this?

2 comments

2 Comments

price.jake1mo ago

Oh man, it's all about the old bricks being softer and more porous (which, you know, makes sense). Portland cement is just too hard and stiff, so it traps everything and the brick's face pops off like a zit. But your grandpa's house from the 1920s might have bricks that are a bit harder or denser, so it works okay for him, or maybe the mortar he used is actually a type N that's a little softer. The line is basically: if your brick crumbles when you scratch it, go with a lime mortar; if it's rock hard, cement might be fine. Honestly, it's a gamble unless you test the brick's strength first.

lisa_grant1mo ago

My buddy @price.jake learned this the hard way when his 1930s fixer upper brick face literally popped off.