Chimney Crown Repair: Seal the Cracks Yourself or Rebuild?
No Sales Tax in any state on every chimney repair product we carry. A cracked chimney crown is the most common way water gets into a masonry chimney, and water is what breaks down brick, mortar and flue tile. Caught early, a crown can be sealed in an afternoon with a brush-on coating. Left alone, it ends in a rebuild. This guide covers how to tell which one you need, how to seal a crown yourself, and how much sealant to buy.
Quick answer: what to use on a cracked chimney crown
- Hairline cracks in a crown that is still solid: brush on CrownCoat chimney crown sealant, two coats. Order the 2-gallon gray or 2-gallon buff pail for a typical crown.
- Working when it's cold: Cold Weather CrownCoat (1 gallon). Standard CrownCoat needs 45°F and up.
- Water also soaking into the brick below the crown: add ChimneySaver water repellent on the brick.
- Crown crumbling, loose or missing chunks: sealant won't hold. The crown needs to be rebuilt by a mason.
All ship with No Sales Tax.
What the chimney crown does
The crown is the slab of concrete or mortar that caps the top of a masonry chimney, around the flue tile. It is shaped to shed rain away from the flue and off the sides of the chimney. It takes more weather than any other part of the house: sun, rain, snow sitting on it, and freeze-thaw cycles all winter.
Most crowns are built from mortar mix rather than proper concrete, and few have the expansion gap they should have around the flue tile. So they crack. Once there's a crack, water runs into it, freezes, expands, and widens it. Every winter makes it worse.
Signs your crown needs attention
- Hairline cracks across the top, or a crack running around the flue tile
- Water stains or white chalky deposits (efflorescence) on the brick below the crown or inside the firebox
- Flaking or crumbling bits of mortar on the roof below the chimney
- Rust on the damper or firebox, or a damp smell from the fireplace after rain
- Spalling brick, where the faces of the bricks are popping off
Check from a ladder or with binoculars, or have a chimney sweep check it at your annual inspection.
Seal it or rebuild it?
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| What you see | What to do |
|---|---|
| Hairline cracks, crown solid when you tap it | Seal with CrownCoat |
| A few wider cracks, crown still solid | Fill the wide cracks first (patching cement or 100% silicone caulk), then CrownCoat over the whole top |
| Brand-new crown | Let it cure 48 hours, then coat it with CrownCoat to keep it from cracking |
| Crown loose, crumbling or missing pieces | Rebuild. A coating can't bond to a crown that isn't sound. |
| Water coming through the brick, not the crown | Treat the brick with ChimneySaver |
How to seal a chimney crown with CrownCoat
CrownCoat is a brushable elastomeric coating. It cures into a flexible waterproof membrane that bridges hairline cracks and moves with the crown as it heats and cools, which is why it outlasts a skim of new mortar.
- Check the weather. The air and the crown must be above 45°F, and it shouldn't drop below that for at least 4 hours after you finish. Keep the coating dry for 4 hours. For colder days, use Cold Weather CrownCoat.
- Clean the crown. Scrub it with a wire or poly brush to get off loose material, moss and dirt. The surface must be sound, clean and dry.
- Fill the big cracks. Fill wider cracks and voids with patching cement or 100% silicone caulk. CrownCoat handles the hairline cracks itself.
- Tape it off. Tape the top course of brick and the flue tile for a clean edge.
- Mist the crown. Lightly dampen it with clean water. Don't leave puddles.
- Apply two coats. Brush on a thin first coat with a 3"–4" synthetic brush. Wait a few minutes until it's tacky, then brush on a second, heavier coat. Work it into the cracks and over the edges of the crown.
Unopened CrownCoat keeps about 18 months. Store it above freezing.
How much CrownCoat do you need?
CrownCoat covers about 40 sq ft per gallon. Measure the top of your crown, including the overhang, and subtract the flue opening.
| Crown size | Area | Buy |
|---|---|---|
| 2 ft x 2 ft | about 4 sq ft | 1 gallon (Cold Weather) or 2 gallons |
| 3 ft x 3 ft | about 9 sq ft | 2 gallons |
| 4 ft x 6 ft (two flues) | about 24 sq ft | 2 gallons |
| Several chimneys, or a contractor | 40+ sq ft | 5 gallons |
The heavier second coat uses more than the first, so round up. Gray suits most concrete crowns; buff suits tan or light brick.
Waterproof the brick too
A sealed crown stops water at the top, but brick and mortar soak up rain on their own. ChimneySaver water repellent is a water-based siloxane that soaks into the masonry and repels water, while still letting moisture from inside the chimney escape. That matters: a film-forming sealer traps that moisture and can make spalling worse. It covers about 125 sq ft per gallon and carries a 10-year warranty. For sizing and step-by-step application, see our chimney sealer guide.
Two more ways water gets in, and how to stop them:
- Down the flue. An open flue takes rain straight to the damper and firebox. A stainless rain cap on a lined chimney, or an Energy Top top-sealing damper on a fireplace flue, keeps it out. The Energy Top also seals in warm air when the fireplace isn't in use.
- Through the flashing. Where the chimney meets the roof, failed flashing leaks into the attic and ceiling. That's a roofing repair, not a crown repair.
Cleaning up the inside
Water stains and soot on the fireplace face come off with ChimneySaver Paint 'N' Peel. You paint it on, let it dry, and peel it off, and it takes the stain with it.
Related guides
- Chimney sealer: how to waterproof a brick chimney
- Chimney caps and liners: what you need, what size, and why
- Chimney liner guide: sizing, insulation and insert relines
- Wood stove flue guide: sizing, flue pipe and when to reline
Not sure whether your crown can be sealed? Email a photo to info@stovesource.com or call 1-888-914-0022. Every chimney repair product ships with No Sales Tax in any state.