How do you repair a chimney, and which repairs can you do yourself?
Short answer. Chimney repair starts with finding which part failed: a missing cap, a cracked crown, failed flashing, eroded mortar, porous brick or a damaged flue liner. A handy homeowner can sometimes install a cap or seal hairline crown cracks from a safe, low roof, but reflashing, repointing, crown rebuilding and relining are jobs for a roofer, mason or certified chimney professional.
Match the repair to the problem
- Rain in the firebox: add or replace the cap; seal or rebuild the crown.
- Stains beside the chimney: new step flashing and counterflashing, and a cricket on wide chimneys.
- A damp chimney breast after driving rain: repoint open joints and apply a breathable water repellent.
- Spalled or loose brick: replace the bricks and fix the water source behind them.
- Smoke, odor or liner damage: sweep, inspect and reline.
- Leaning or separating: a structural evaluation, often by a mason or engineer.
What a homeowner can reasonably do
- Install a bolt-on cap on a single flue, if the roof is low, dry and walkable and you use fall protection.
- Brush an elastomeric crown sealer over hairline cracks.
- Apply a breathable siloxane water repellent to sound brick. Avoid paint or non-breathable sealers, which trap moisture and spall the brick.
- Trim branches back from the chimney.
What to leave to professionals
- Reflashing. Step flashing has to be woven into the shingle courses and counterflashing cut into the mortar. Tar and caulk over failed flashing buys a season at best.
- Repointing. Joints need the right depth and a mortar no harder than the brick.
- Crown rebuilds and any work on steep or two-story roofs.
- Flue liners, which affect fire safety and carbon monoxide.
A hose test, one area at a time, is the best way to confirm the source before you spend money. See chimney leaks and crickets and roof flashing explained, and Robust Roofing's guide to why chimney flashing fails.