Mortar from around chimney bricks being “pushed” out
renovationgirl
| Posted in Construction Techniques on
Up on roof to clean. Noticed pieces of mortar lying on roof next to chimney. Upon further inspection, mortar,, in some areas, has base behind mortar that looks like it is swelling until the mortar falls out. What’s going on and /or how do I fix and prevent?
Replies
Not at all unusual for the top of a chimney. Not sure how much is due to a sort of "frost heave", how much is due to certain chemical reactions, and how much is due to the heat/cool cycle and associated "creep".
Basically, you get the chimney pointed. And having the top around the flue remortared with a proper slope to shed rain helps.
Reno
look at the top (wash) of the chimney cap closely, where the flue pipes come out. There should be a good seal around the flues (in addition to the proper slope of the cap).
i use urethane caulk at that joint. This with clay flue liners.
with a metal pipe it's usually a hi temp silicone.
If moisture is degrading the morter and "forcing it out", I'd take a good look at the top.
How old is the chimney? Not unusuall at all for old chimney mortar to start spalling from weather. It also sounds like it may have been repointed at some time and the new mortar is what's falling out. Either way I'd get a masons opinion.