The mortar in our 25-year-old chimney is starting to crack and now leaks into our home if it rains hard.

I assume we're probably in need of repointing, but a contractor that has done roof work for us before says that caulking in some silicon into those cracks will do the trick.

Is that an acceptable solution? Or will we just be dealing with this again in 6 months?

Want to make sure they're not just trying to make a quick buck.


This is the same question you asked a couple of days ago. BTW, NEVER use silicone caulk on chimney masonry cracks, especially if the crack passes through. There are special masonry high temp caulks for this purpose. In your case where water is passing completely through the brick joints, you really need to have it repointed. Any competent contractor would not suggest silicone in this case. Find a new contractor.

  • BTW, is your chimney lined with tile? Rain cap? – shirlock homes Feb 5 '11 at 14:10

Filling cracks in mortar with silicone sealant won't last very long. It might last longer than 6 months but I wouldn't expect it to last a 2nd winter.

You need to get the brickwork properly repointed.

It sounds like they're after charging you twice - once for the caulking and then again for the proper job, for which they will probably charge top price.

Get another couple of quotes and take it from there.


Never even think of using silicone-based compounds for anything like a chimney unless they are specifically declared to be fireproof.

About one month ago I was replacing silicone sealant on my window and out of curiosity I tested how flame-resistant it is. I cut a small piece about 5 millimeters in diameter and about 100 millimeters in length, brought it into bathroom and tried to set it on fire. Well, it took maybe two seconds of heating it with a match to set it on fire and then it burned as if it was a Bickford fuse, just slower. I couldn't even blow the flame out - I had to flood it. I learned a lot there.

You should use some cement-based mortar - either some special variety designed for chimneys, or just general purpose one used for building brick walls.

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