Chimney crown
Also called: crown, chimney wash, mortar wash, chimney top, crown seal, crown coat, concrete chimney cap
The concrete slab that caps the top of a masonry chimney around the flue tile, sloped to shed water and overhanging the brick with a drip edge. When it cracks, water enters the brick and the joints, liner and flashing fail in turn. Sealed for $200–$700 if intact, recast for $1,000–$3,000 if not.
Everything a chimney does to keep water out starts at the crown. Done right, it’s a cast concrete slab 2–3 inches thick at the edge, reinforced, sloped from the flue tile outward, overhanging the brick by an inch or two on every side with a drip groove underneath so water falls clear of the wall, and separated from the flue tile by a bond break so the tile can expand without cracking the slab. Done the way most tract-house chimneys were done, it’s a “mortar wash” — an inch of the mason’s leftover mortar troweled across the top, flush with the brick, no overhang, no reinforcement — which cracks in the first few winters and channels water straight down the outside of the brick.
The crown’s failure is usually the first one on a chimney and the one that causes the rest. Water enters the cracks, freezes, widens them, soaks the top courses of brick, opens the mortar joints, spalls the brick faces, and eventually runs down inside the chase to the flashing and the ceiling. Bits of the crown in the gutter, white staining on the top courses, and water in the firebox after rain are the symptoms.
Two repairs. An intact crown with hairline cracks is cleaned, the cracks filled, and the whole top coated with a brush-on elastomeric crown sealer — a DIY job from a walkable roof and a sweep’s half-day. A crown that’s crumbling, missing pieces, or was never more than a wash is broken out and recast in a form with rebar, a slope, an overhang and a drip edge — a mason’s job. The cost page has both, and the DIY guide covers the seal.