Caring for the Outside of Your Chimney
While it's important to care for the inside of your fireplace, chimney, and damper, don't forget the outside as well.
A chimney can be either an exposed pipe, a framed enclosure that is covered with siding ("a sided chase") that houses the flue pipe, or a masonry chimney. In all cases, the chimney travels from the inside of the home to the outside either through an attic and roof or out a wall. The point where the chimney exits the structure is a primary source of leaks. Thus, the flashing that surrounds this location should be water-tested (as should all other flashing) using a garden hose to make sure that it is in good condition and leak-free.
If your chimney is "in the buff," the metal pipe can be attacked by rust and the joints can become loose. Use a wire brush to remove the rust. Prime and paint the rusted area with high-temperature paint. Use a screwdriver to tighten screws at all connections. Install new self-tapping sheetmetal screws at locations where screws were previously installed and worked loose. Remove an existing screw and use it as an example when purchasing replacement screws.
Masonry fireplaces have a unique flashing detail called a masonry counter flashing. This secondary piece of flashing covers the primary flashing that is immediately adjacent to the roofing. The counter flashing has a slight lip that is inserted into a mortar joint and then either mortared or caulked into place. The caulking or mortar should be water-tested annually and should be repaired or replaced as needed.
A coat of paint helps to hide otherwise unattractive flashing and prevents it from deteriorating quite as rapidly.