Crown Coat
A crown coat is the sloped mortar or cement cap that sits at the top of a masonry chimney, surrounding the flue tile(s). It is not the decorative cap piece (that's a chimney cap) — it is the poured or troweled waterproof seal that directs rainwater away from the flue and the chimney's interior bricks. A properly built crown coat is two inches thick at the flue, tapered outward to a drip edge overhanging the brick by about two inches, and cast from a waterproof mortar mix or a specialty elastomeric crown-coat product.
In depth
Over time, crown coats crack from freeze-thaw cycles, especially in Wisconsin's climate. Those cracks let water seep into the chimney wall, where it freezes and progressively spalls the brick from the inside out. Before any exterior chimney cleaning or sealing, we inspect the crown coat — cleaning a chimney whose crown is failing is cosmetic at best and speeds the damage underneath. Sealing or rebuilding a crown is a masonry specialty job.
How this shows up on our jobs
Every chimney we clean in Madison gets a crown-coat inspection first. If it's cracked, cleaning alone doesn't stop the damage — you need to rebuild or seal the crown before the wash.
Services where this matters
Related terms
Chimney Cap
A chimney cap is the metal (stainless, copper, galvanized, or aluminum) or cast-stone hood that sits on top of the flue, typically with a mesh screen on the sides. It serves three functions: it keeps rain, snow, and animals out of the flue; it acts as a spark arrestor; and it stops downdrafts that can push smoke back into the home. It is not the same thing as a crown coat — the cap sits on top of the flue tile, while the crown is the cement seal around it.
Damp Proofing
Damp proofing is the application of a moisture-resistant coating or membrane to a masonry surface — most commonly foundation walls, brick veneer, and chimneys — to slow water absorption and reduce efflorescence, spalling, and interior moisture problems. It is less robust than true waterproofing (which forms a continuous, pressure-rated barrier) but more cost-effective and better-matched to surfaces that need to breathe.
Efflorescence
Efflorescence is the white, chalky, powdery deposit that forms on the surface of brick, concrete, stone, stucco, and block masonry when water dissolves mineral salts inside the material and carries them to the surface. As the water evaporates, the salts are left behind as a crystalline residue. It is cosmetic — not structural — but it is frustratingly persistent because every rain cycle can push more salts to the surface.
Polymer Sealer
A polymer sealer is a protective coating applied to a cleaned and dried surface — glass, concrete, wood, metal, brick — that forms a long-molecule chain on the surface to repel water, dirt, and staining. In window cleaning, glass-specific polymer sealers (often silicon-dioxide based, sometimes called "glass coats" or "hydrophobic treatments") cause rain to bead and sheet off, which keeps windows cleaner 2-3x longer between professional cleanings. On concrete, acrylic or urethane sealers protect against oil, rust, and de-icing salt.