Switched from lime mortar to Portland after a failed repair job and wish I did it sooner

I had this old chimney cap that kept crumbling no matter how many times I patched it with lime mortar. Last fall I finally bit the bullet and used a Type N Portland mix instead. That cap's been solid through two winters and a wet spring. My granddad always swore by lime for historic stuff but for modern brick this just works better. Anyone else make the same swap and get better results?

3 comments

3 Comments

aaron67714d agoTop Commenter

Hold on though, Barbara has a point about the hardness mismatch. Portland is significantly stiffer than most historic bricks, and that difference can absolutely cause spalling if there's any moisture getting behind it. A year of good weather isn't enough to prove it's safe long term, especially on something like an old chimney that sees a lot of freeze-thaw cycles.

skyler_anderson6514d ago

Man I used to be totally against Portland for anything... my old boss drilled it into my head that lime was the only way to go for any kind of brick work. But then I had this old retaining wall that kept spalling every winter after I repointed it with lime mortar. Finally tried a Type N Portland mix last spring and it's been through two hard freezes with zero cracks. That wall would have needed patching again by now with lime... sometimes tradition just doesn't beat what actually holds up.

barbara_taylor8314d ago

Yeah but isn't the whole point of lime that it's supposed to be softer and more flexible than the brick? I mean if you put a hard Portland mix on old soft brick or stone, aren't you basically trapping moisture inside and making the brick itself spall instead? A year is not really that long to judge either, in my book old school repointing was always meant to last decades not just a season or two. Maybe that wall was just a bad candidate for lime in the first place, but idk, I still think Portland is asking for trouble on anything built before 1920.