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I have a client who has a salt box house with a 4ft by 4ft chimney in the center of it. The chimney has had the mortar cap around the 2 flue liners replaced 3 time in 10 years. Within 12-18 months the cap cracks and water leaks into the brick and into the house. The cimney was torn down below the roof line 2 years ago and re-laid, but the cap has cracked again. There is nothing being vented into the chimney and the fireplace has never been used. I have been told by the local masonry supply house that a chimney this size should have a cement not a mortar cap but the mason that relaid it says this is not so. We have also considered having a copper cap made to cover the top of the chimney that would slip over the top 3-4 inches. Any suggestions would be greatly appreciated.
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I like the copper cap idea. Pretty and keeps the weather out of the cap below. Easy to do in the cold weather, too. FHB ran an article a few years ago on how to do a bombproof masonry cap. Maybe search for it?
Bill
*Issue #117, page 76. Bill
*About 99% of the chimney caps I look at are cracked and about 99% of them have been poorly made: not thick enough (often the "mason" feathers them out to nothing at the edges), no overhang, and I suspect the mortar or concrete has not been properly cured.I i think there's a relationship there. I rarely see a properly formed cap with cracks other than hairline cracks.
*Bob, The mason kept the last cap covered for several days after he did it. It appears to be about 1 1/2 inches thick on the edges. The things is cracked in about 10 places even the center side to side. I am at a loss as to what is causing this, other than the fact that I do not think mortar can hold up on this large of an area. Any other thoughts? Thanks Jim
*we use concrete caps 2 inches thick at the edge sloping up to the flues..rake a caulk joint at the flue for a masonry caulk...
*I have done a lot of these----1,2,3 and even one 4 flue but nothing 4 ftx4ft.I use mortar,not concrete.I tint the mortar to match the existing mortar joints and to take the new grey color out of the new cap.On a really big one I try to put something in the middle of the cap to act as re-bar.A lot of times it is chicken wire or really coarse hardware cloth.I usually do them about 3-4 inches thick with a very steep taper around the edges. It tapers from about 3 inches to 0 in about 2-3 inches.I like my mortar caps to look like itty-bitty hip roofs.Isolate the mortar from the flue with a couple of quick wraps of that insulation that goes between the sill and the foundation. after the mortar sets up,trim the insulation down just below the surface of the mortar and Geocel the gap.I love installing mortar caps and chimney caps.It is a nice little extra touch that you can often sell to the homeowner as an "extra" in the middle of the job.
*b WBA At Your ServiceWe (or one of our roofers) use sheet lead or lead coated copper for our caps. They last 50 to 100 years depending on the weather. And they don't crack. What is the appeal of a masonry cap ? Price ? What about after you have replaced it 2 times in 10 years ?
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I have a client who has a salt box house with a 4ft by 4ft chimney in the center of it. The chimney has had the mortar cap around the 2 flue liners replaced 3 time in 10 years. Within 12-18 months the cap cracks and water leaks into the brick and into the house. The cimney was torn down below the roof line 2 years ago and re-laid, but the cap has cracked again. There is nothing being vented into the chimney and the fireplace has never been used. I have been told by the local masonry supply house that a chimney this size should have a cement not a mortar cap but the mason that relaid it says this is not so. We have also considered having a copper cap made to cover the top of the chimney that would slip over the top 3-4 inches. Any suggestions would be greatly appreciated.