Chimney caps are cement structures located at the top of a chimney. Not only do they add a decorative element to a chimney but they can also be used to protect the structure from rodent intrusion. If your chimney cap is broken and needs to be repoured, these steps will help you create a solid cap that will last for years to come. Before you begin this process you should make sure your existing chimney cap has been removed.
Build a wooden frame to pour the new concrete in. Use a 2 by 4 foot board and rip it with a 15 degree bevel. Nail the board to a 1 by 6 foot board making sure the square end is flush with the bottom. Cut it into four sections so the 2 by 4s fit tightly around the top bricks of the chimney. Screw the four sections together and use duplex nails to reinforce it. The nails should go through each section from the outside allowing them to just graze the bevel.
Place your form on the top of the chimney allowing it to rest on the nails. Use duct tape to fill in any holes in the form to prevent cement from leaking.
Wrap the flue tiles with cardboard and secure the cardboard with more duct tape. Oil the outside of the cardboard and the inside of the frame to prevent them from sticking. Don't get oil on the top of the bricks or the concrete will not bond to the top of the chimney properly.
Mix the concrete on the ground and haul it onto the roof in 5 gallon buckets. Pour enough concrete into the frame so that it is about 1 inch above the top of the bricks. Use a trowel to smooth out the concrete.
Cover with a sheet of plastic to protect the area as it dries. When dry, carefully disassemble the frame.
Add rebar to the cement about halfway through the pour to add strength.