As the chimney is being built, the inside of the chimney must be filled with brick. In the case of this picture, bricks must seperate two different flue liners.
Nails are hammered in where the form will rest on the brick on your chimney. The nail heads are snipped off so the nails can be removed when its time to strip the form.
Coaxial cable is used to form what would be the drip edge. The cable is stapled in place, and the staples are hammered down flat.
The concrete is reinforced by metal that is imbedded in the form. Foam is wrapped around the flue liners to add a 10 mm gap between the flue liners and the concrete. Concrete that directly touches the flue liner can damage the flue liner when the concrete expands and contracts.
The bottom of the cap, where the concrete meets the brick is caulked to finish the cap off!
The gap between the flue liners is caulked with a polyurethane caulk. For any masonry application or for exterior applications Tundra Masonry uses polyurethane caulk.
The form is put in place and a sticky waterproof membrane called Blue Skin is used to act as a "bond break" so the concrete does not bond to the brick below. This prevents the concrete which is a much harder material than the brick from cracking the brick when the concrete expands and contracts. The Blue Skin also acts a moisture barrier.
Once the chimney is built up with brick, a form is made out of straight sturdy two by four lumber to a quarter inch wider dimensions than the chimney is. The Form is constructed with screws so it is easier to uninstall.
How Tundra Masonry Installs a Concrete Chimney Crown.
The procedure of installing a concrete chimney cap is slowly being lost in time. Metal caps are becoming more and more popular. It is quicker and easier to install a metal cap. With a concrete cap you have to wait a week for the concrete to cure before stripping the wood form used to pour the concrete in. If you were repairing the brick under the cap you may also have to wait a day before starting to form and pour the cap becasue the weight of the concrete may move or displace some brick. The installation of a metal cap can be finished the same day the mason finishes repairing the chimney. However there are a lot of advantages of a concrete cap over a metal cap which is the reason why Tundra Masonry prefers investing the extra work.
The Time Honoured Procedure of Installing a Concrete Chimney Crown