How to Cement a Chimney Cap

A chimney cap is necessarily exposed to the elements on a regular basis. Because of this, the mortar supporting it can become chipped or break over time. At times, it will be necessary to add additional cement to the chimney cap to help stabilize it. 

Directions:

1. Using a hammer and chisel, remove any mortar remaining on the cap. Make sure that all of the mortar is gone. This can be done with a wire brush.


2. Apply membrane flashing, making sure that it goes from the brick face along the sides of the liner for the flue.


3. Create an expansion joint, which will stop the cement from making contact with the flue. A simple method of doing so is to wrap a pad around the flue. The pad should be at least a half-inch thick.


4. Using 2x4 lumber, build a frame so that there is a short side that is cut at a fifteen degree angle. This angle is important because it will help rain to drain properly from the bricks on the chimney. Nail the four boards together, which will create the frame's base. You will then need to screw the 1x6 boards so that they are upright, and also flush against the lower part of the 2x4 frame. This will create the frame's walls.


5. Nail duplex nails into the 1x6, and just above the 2x4 at its highest point (which will allow the angle for the cap). Put the chimney frame on using screws, but make sure that the screws extend out an inch or more and that they are placed in position eighteen inches apart. The screws will support the chimney frame when it rests on the top row of bricks. Make sure that the cracks between the frame and the chimney are covered.


6. Cut some rebar so that it is four inches shorter than the frame's width. Two pieces of rebar can be used for each side of the flue.


7. Mix the cement and make sure it is in position on the roof.


8. Make sure that the base of the chimney pad is moist, and pour the cement. Make sure that the cement angles out properly. Lay the rebar along the frame's width once the cement is one inch above the rim of the brick. Make sure to center the bars in between the flue and the frame ends.


9. Pour the remaining cement, making sure to add additional cement near the flue. Use your trowel to smooth out the cement in a slight angle downward. This will establish the draining surface. Let the cement dry overnight.


10. Pull out the frame and pad for the flue. Caulk around the flue with high temperature caulk to make sure that any gaps in the flue are properly filled with the caulk. Make sure that the cement is waterproofed.