Last fall I put a completely new concrete crown on my chimney. This was in preparation for a new PE Super insert and insulated SS liner (for which this forum was an invaluable resource). Most of the Internet articles I found on the subject just involved slapping a layer of mortar around the flues, which was not the route I wanted to take. So I figured I'd document my project here in the hope that it may help someone in the future. I relied heavily on this PDF article for the basic process.
My old crown was in very bad shape. I’m not sure if it was original to the house (built in ’74), but it was poorly constructed and allowing water to seep into the brick. My chimney is quite large, about 6 ft x 2 ft, so I wasn’t able to capture the entire thing in most of the pictures. Removing the old crown was quite easy; most of the chunks came off without much effort. I also took off the top course of brick because the top of the flue needed to be several inches above the top course so the crown could be sloped down for drainage.
I built a welded steel frame from angle iron to support the new crown. The ends are notched to allow the pieces to rest on the brick. Building and mounting the concrete form was probably the most time-consuming part of the whole project. It is constructed of 2x4 and 1x6 material, providing a 1.5” overhang around the entire chimney. I beveled the top side of the 2x4’s at a 15 degree angle in order to create a drip edge, so that water could not flow around the crown and end up running down the brick. Once the form was in place, supported on my scaffold, I attached sections of waterproof cement board to the steel frame and covered all the joints with flashing tape. The article I referenced above emphasizes that is important to create a “bond break” between the brick and concrete, so they can shift relative to each other. I also wrapped the two flues with cardboard.
I had never worked with concrete much before, but it turned out to be fairly straightforward. Since I was working 20 feet up in the air, I pulled up my garden hose and mixed about 400 pounds of concrete in a 5-gallon bucket using a paint mixing attachment on the end of my cordless drill. Not the best setup but it got the job done. When the form was about half full, I added a layer of 1”x1” steel wire mesh for reinforcement. As you can see from one of the photos, the unfortunate thing about working with concrete is that once you start, you have to keep at it until the job is done. I did my best to angle the surface away from the flues for proper drainage.
I removed the form about four days later. Everything looked good except that there was some bad pitting around the sides where the concrete had not filled in very well. It was mainly a cosmetic issue, but in hindsight I probably would have used a smaller-aggregate concrete and/or vibrated the form during the pour. I ended up applying two coats of Thoroseal, which is a thick cement-based coating that can be applied with a stiff brush. It fills in all the pitted areas and also acts as a sealer. At this time I also removed the cardboard from around the flues and filled the gaps with backer rod and silicone sealant.
Overall I was happy with how it turned out. Hopefully it will outlast me… it’s not a job that I want to repeat! If others have done similar projects, I would love to hear your experiences.
-John
My old crown was in very bad shape. I’m not sure if it was original to the house (built in ’74), but it was poorly constructed and allowing water to seep into the brick. My chimney is quite large, about 6 ft x 2 ft, so I wasn’t able to capture the entire thing in most of the pictures. Removing the old crown was quite easy; most of the chunks came off without much effort. I also took off the top course of brick because the top of the flue needed to be several inches above the top course so the crown could be sloped down for drainage.
I built a welded steel frame from angle iron to support the new crown. The ends are notched to allow the pieces to rest on the brick. Building and mounting the concrete form was probably the most time-consuming part of the whole project. It is constructed of 2x4 and 1x6 material, providing a 1.5” overhang around the entire chimney. I beveled the top side of the 2x4’s at a 15 degree angle in order to create a drip edge, so that water could not flow around the crown and end up running down the brick. Once the form was in place, supported on my scaffold, I attached sections of waterproof cement board to the steel frame and covered all the joints with flashing tape. The article I referenced above emphasizes that is important to create a “bond break” between the brick and concrete, so they can shift relative to each other. I also wrapped the two flues with cardboard.
I had never worked with concrete much before, but it turned out to be fairly straightforward. Since I was working 20 feet up in the air, I pulled up my garden hose and mixed about 400 pounds of concrete in a 5-gallon bucket using a paint mixing attachment on the end of my cordless drill. Not the best setup but it got the job done. When the form was about half full, I added a layer of 1”x1” steel wire mesh for reinforcement. As you can see from one of the photos, the unfortunate thing about working with concrete is that once you start, you have to keep at it until the job is done. I did my best to angle the surface away from the flues for proper drainage.
I removed the form about four days later. Everything looked good except that there was some bad pitting around the sides where the concrete had not filled in very well. It was mainly a cosmetic issue, but in hindsight I probably would have used a smaller-aggregate concrete and/or vibrated the form during the pour. I ended up applying two coats of Thoroseal, which is a thick cement-based coating that can be applied with a stiff brush. It fills in all the pitted areas and also acts as a sealer. At this time I also removed the cardboard from around the flues and filled the gaps with backer rod and silicone sealant.
Overall I was happy with how it turned out. Hopefully it will outlast me… it’s not a job that I want to repeat! If others have done similar projects, I would love to hear your experiences.
-John
