Chimney Doctors' Homeowner's Guide
Failing Concrete Chimney Caps
Weather conditions play major factor in failing chimney caps (i.e. Rain, snow, freezing, thawing and heat). Durability of masonry is the main reasons chimney caps have lasted for many years.
Causes for failure
Click on photo to enlarge
- Most exposed and only horizontal surface
- Area most likely to absorb water
- Flashing is not properly installed
- Same mortar used as when brick were laid
- Application is put on too thin
- Directly bonded too flue tile
- Concrete shrinks as it cures
- During curing process cracks form
- Mortor around chimney should be tapered to a feather edge
- Thin edges cannot hold up in severe weather
- Deterioration occurs and starts to collect water
- Cap is rarely isolated from flue liner
- In winter months; flue tiles expand in upward direction
- Cap is bonded to frozen exterior bricks
- Connected caps during flue expansion can crack
These conditions ultimately allow water to get in thru cap. Every year that deterioration occurs, more damage is done to the top of the chimney and to the cap. Eventually, water can make it's way into the house and cause severe damage at large.
Wisconsin Administrative Codes States...
(8) CHIMNEY CAPS. Chimneys shall be provided with precast. or cast-in-place concrete chimney caps. Chimney caps shall have a minimum thickness of2 inches, shall slope outwards away from the flue, and shall provide a one-inch overhang and drip edge on all sides. A slip joint shall be installed between the flue and the cap. The slip joint shall be filled with 1/4-inch felt or similar mate- rial and shall be caulked with high-temperature caulk or similar material to prevent water infiltration.
(Issued May - 2005)
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Chimney Doctors provides chimney and fireplace services to the following Southeastern Milwaukee & Southcentral Madison Wisconsin Communities:
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