· by Michael Blair, Nashville's Masonry
A chimney is exposed on four sides and on top, with no roof over it and nothing sheltering it. That makes it the fastest-weathering masonry on most Nashville houses.
The crown
The concrete cap on top should be a proper sloped crown with an overhang and a drip edge, not a thin skim of mortar. A cracked crown lets water straight into the chimney structure.
Thin mortar washes are extremely common on older houses and they crack within a few years.
Flashing at the roof
Where the chimney passes through the roof, step flashing should be woven into the shingle courses and counter-flashing let into the mortar joints.
Sealant smeared over the junction is the common cheap repair and it fails in a few Middle Tennessee summers. This is the most frequent source of a chimney leak.
- A proper sloped crown with overhang and drip edge
- Step flashing woven into the courses
- Counter-flashing let into the mortar, not surface-sealed
- A rain cap over the flue
- Repointing the exposed upper courses first
The flue and the cap
An uncapped flue takes rain directly into the chimney, which damages the liner and the smoke chamber and brings moisture into the house.
A cap with a spark arrestor also keeps birds and squirrels out, which is a common Nashville problem in spring.
Leaning and separation
A chimney pulling away from the wall, or visibly out of plumb, is a structural matter rather than a weathering one, often from footing settlement.
A visible gap at the wall junction that has widened is worth an assessment rather than a caulk gun.