How to Pour Concrete Chimney Caps

Chimney caps are made of cement and are on top of the chimney. Their primary purpose is to keep small animals and rodents out. However, they can also provide an architectual element, depending on the design. When it's time to replace a chimney cap, here's how to do it.

Supplies

• 2 x 4 inch board 


• 1 x 6 inch board


• Nails


• Screws 


• Duct tape


• Cardboard


• Oil


• Cement mix


• Five gallon bucket


• Trowel


• Large plastic sheet

1. Remove the old chimney cap


2. Set up the new frame from the wood in which to pour the new concrete cap. You will use the 2 x 4 inch board and 1 x 6 inch board for this.  Use your saw to cut to the dimensions of the old chimney cap. Attach the 2 x 4 inch board to the 1 x 6 board together with the nails.


3. Measure the top around the chimney bricks.


4. Cut the board into four pieces. It must fit snugly around the top bricks of the chimney. This will be your concrete mold.  Reinforce the sections by adding screws. 


5. Plug any potential holes in the form with duct tape.


6. Cover the flue with cardboard and tape it down tightly, also with the duct tape. This will prevent cement from entering the chimney, so make sure it is secure.


7. Apply your oil to the outside of the cardboard and the inside of the frame around the chimney. This will stop the cement from sticking to them.  Important: do not get oil on the chimney bricks, or the concrete will not adhere to the chimney top!


8. Use a five gallon bucket to mix the concrete at ground level, then transport it to the roof where it will be used. Prepare the mix according to the manufacturer's directions.


9. Pour the concrete into the frame. The frame should be filled one inch taller than the existing brick. Trowel out the concrete to make it smooth. Cover with a sheet of construction plastic to protect it from moisture until it is cured.


10. Depending on weather conditions, allow up to seven days.


11. Remove the frame.