Chimney caps are an essential part of a well built structure. Caps enclose the structure, and prevent water from entering and causing further damage. Once it is damaged or cracked, it should be replaced as soon as possible, or you may end up having more serious damage to the chimney. Here are the three types of caps that you will see on most homes:
Formed and Poured Caps:
This is the most common type of cap for larger chimneys. Lumber or steel is used to create a form on top of the chimney, and high strength concrete is poured in, normally about 4 inches. We pour are caps 5.5 inches thick, reinforced with rebar. We also include an expansion joint for each flue, and where the cap meets brick. Expansion joints prevent the from cracking by allowing expansion during freeze thaw cycles. Once the concrete cures, the forms are removed.
Caps should be pitched from the center and have approximately 2″ overhang to provide proper water run off. We additionally form a drip edge into our caps which is and indentation on the underside of the overhang. This allows water to drip off the cap rather than down the face of the brick or stone.
Another common type of chimney cap is a prefab. These are prefabricated by a manufacture and purchased at brickyards by masonry contractors. Once the old cap is removed, a prefab is set in a bed of mortar on top of the chimney.
These are used for smaller chimneys and come in 3 common sizes to match your flue size. 8×8”, 8×12”, and 12×12”.
Trowel On – Mortar/Concrete:
This is a common type of cap found in newer subdivisions. Home builders use this type because it is faster and more cost effective than a form and pour. Excess mortar or concrete is simply troweled on top and smoothed out to enclose the brick. The mortar is pitched from the center to prevent water from sitting on top of the chimney.
The disadvantages of a trowel on is they are much thinner and don’t last as long as a form and pour. Additionally, they have no overhang to prevent water from running down the face of the chimney.