Dear Askthechimneysweep: I have questions regarding my brick chimney construction; I am having a leak near my chimney and my chimney service man says that it is because of the corbel having exposed brick holes. What is a chimney corbel and is it a repair that I can do myself?
Thanks, Larry Fields – Columbus, OH
Larry,
The corbels on a chimney have the potential to be very bothersome to homeowners when it comes to water problems. Whether it be exposed brick holes or poor design, corbels certainly have the capacity to cause problems. The chimney’s corbel is also called a 
shoulder or hip and is shaped the way that it is to make room for the smoke chamber inside the chimney flue. Chimney leaks caused by corbels are often easy to diagnose but not always as easy to fix. Let me explain.
Whoever came out to take a look at your chimney diagnosed a chimney problem that we see all too often. It is not often that a chimney’s construction is ultimately its downfall when it comes to water problems. When bricklayers construct the chimney’s corbel and leave the brick’s holes exposed to hold water, as pictured, the water can actually saturate through the brick, wearing away quickly at any water repellents which may have been placed as a precaution, causing water to enter the home.
These exposed brick holes cause chimney leaks which can only be fixed if a slate or concrete cap is installed over the existing “stair stepped” bricks after they are cleaned, creating a smooth surface where water cannot pool, and finally waterproofed. Mold tends to grow where water pools, and these brick holes are the perfect area for mold to grow undisturbed creating an unsightly look the the chimney. A chimney shoulder or corbel should be smooth and allow water to run off instead of pool. Wherever water pools, whether it be on a corbel, a chimney crown, or any other horizontal surface on the home, there is a high likelihood of a water problem occurring.
A chimney corbel is one of the chimney construction details that may sometimes be overlooked by an inexperienced builder that causes more trouble than its worth. If a corbel is constructed such that its top is flat and builder does not smooth the top of the corbel completely there may be small depressions in the surface which allow water to pool. In situations like these the likelihood is for the corbel to crack instead of cause a water problem. Weather here in Ohio is unpredictable. Just this winter we would be almost in the 60’s one day and then below freezing the following weekend. Freeze-thaw damage is a real killer of masonry structures like a chimney where water is able to pool. An insignificant hairline crack is far from insignificant by the time the season is over and it will only continue to grow over time.
As to whether or not this is a repair you can conduct at home, I would have to say more than likely not. Since you’re dealing with a sloped surface installing a concrete cap over the exposed brick is not practical for a do-it-yourselfer to do. I would let the professional handle this project but go to the negotiation table knowing exactly what type of work he should be performing. As always, get more than one estimate from licensed chimney contractors in your area to ensure that you are getting the highest quality work for your money.