How to Cement Chimney Caps
A chimney cap, or crown, is a structure that fits on the top of a chimney. Its primary purpose is to prevent water from leaking into the chimney, which can cause the chimney to crack when the water freezes. Homeowners with masonry experience can construct a chimney cap with mortar.
Things You Need:
- Chisel
- Wire Brush
- Membrane Flashing
- Plastic grocery bags
- Duct tape
- 2x4-inch wooden boards
- Wood screws
- Screwdriver
- Cement
- Trowel
- Rebar
- Scrap wood
- Caulk
- Caulking gun
Instructions:
- Remove any existing mortar from the top of the chimney with a chisel and wire brush. Install membrane flashing to the sides of the flue lining.
- Wrap plastic grocery bags around the flue to serve as an expansion joint for the chimney cap. This expansion joint should be at least 1/2 inch thick and extend at least 8 inches up the chimney. Secure the expansion joint in place with duct tape.
- Construct a wooden frame to serve as a mold for the chimney cap. The sides of the frame should form a 15-degree angle to drain water away from the chimney. Hold the frame together with wood screws that protrude from the wood by at least one inch.
- Place the wooden frame onto the chimney so that the screws support the frame. Add additional support with a series of clamps and fill the space between the chimney and the frame with scrap wood.
- Moisten the expansion pad to prevent it from sticking to the cement, and pour wet cement into the frame until it is one inch over the rim of the chimney. Place lengths of rebar into the cement for support, so that each piece of rebar is between the frame and the flue.
- Shape the cement with a trowel so that slopes downward slightly as it reaches the edge of the frame. This will allow rain to drain away from the chimney.
- Allow the cement to dry overnight. Remove the wooden frame, grocery bags and clamps from the chimney cap. Seal the gap between the chimney cap and the chimney with caulk, and apply a waterproofing compound to the chimney cap.