How to Replace a Cement Top on a Chimney

Measure your chimney at the base of the existing chimney cap. Use a tape measure to measure all four chimney sides. Add 2 1/2 inches to each measurement to allow for chimney cap overhang over the sides of the chimney for proper fit.

Break off the existing cap to remove it from the top of your chimney. Use a hammer and chisel to chip the cap away from the chimney flue. Use light strikes on the chisel with the hammer around the flue to avoid damage to the flue beneath the cap. Continue to chip away at the cap until you reach the brick of the chimney itself.

Remove any mortar remaining on the chimney, after removing the cap, with a wire brush. Scrub away the mortar with the brush using a vigorous back and forth motion.

Raise the new chimney cap over the flue and lower it onto the top of the chimney. Use a helper to aid you in lifting the heavy cap into place. Level the cap out over the top of the chimney.

Stuff the space between the base of the cap and the chimney flue with mineral wool. Add a fire-rated silicone caulk to the wool to help it stay in place, then place a thick bead of the caulk in the joint between the cap and the chimney to complete the installation process.