Can a chimney leak through the brick?
Short answer. Yes. Brick and mortar are porous and absorb rain, and a chimney with worn mortar joints, a cracked crown, spalling brick or no cap can soak up enough water to leak into the attic or the house. Brick leaks are often mistaken for flashing leaks, so it pays to identify which one you have before paying for a repair.
How water gets through masonry
- Absorption. Brick soaks up rain like a stiff sponge. In a long Georgia downpour, a tall chimney can absorb a surprising amount.
- Mortar joints. Mortar wears faster than brick. Cracked, sandy or recessed joints let water straight in.
- The crown. The concrete or mortar top of the chimney sheds water away from the flue. Cracked crowns, or thin mortar washes that were never a proper crown, let water into the core.
- No cap. Rain falls straight down an uncapped flue.
- Spalling. When wet brick freezes, its face flakes off, exposing softer brick. More common in the North Georgia mountains.
Signs it is the brick, not the flashing
- White, powdery efflorescence on the brick, inside or out, which is salt left as water passes through.
- Dampness on the chimney masonry in the attic above the roofline flashing.
- Leaks that continue for a while after the rain stops, as the soaked brick drains.
- Stains on all sides rather than just one side or the uphill face.
What fixes it
- Repointing worn mortar joints.
- Repairing or rebuilding the crown with an overhang that drips clear of the brick.
- Installing a cap to keep rain out of the flue.
- Applying a breathable, water-repellent treatment made for masonry. Avoid paint or film sealers that trap moisture inside and make spalling worse.
- Replacing badly spalled brick.
Flashing leaks look different and are covered in chimney leaks and crickets. Also see common roof leak causes.