Local Chimney Crown Repair in Jacksonville

What the code asks of a chimney crown

The crown is the slab that covers the top of a masonry chimney around the flue. Florida Building Code, Residential section R1003.9.1 asks for a concrete, metal or stone cap, sloped to shed water, with a drip edge and a caulked bond break around any flue liners, per ASTM C1283.

A flat top holds water. A top with no drip edge lets water curl back under the slab and down the faces. A top cast tight to the flue tile cracks when the tile heats up. The crown takes the weather straight on, so it gets a close look at the yearly soundness inspection NFPA 211 sets for chimneys.

Mortar wash, cast crown or precast slab

Some chimneys are topped with a mortar wash, which is bricklaying mortar troweled into a shallow cone that thins to a feather edge at the brick. The Brick Industry Association's Technical Note 19B describes a cap that is precast or cast in place to a set shape, and it warns against feathering a cap to its edge because the thin edge deteriorates sooner.

A cast crown is formed and poured to a set thickness with reinforcement, an overhang and a drip groove. A precast crown is made on the ground and set on a mortar bed. Your estimate names which of the three you have, because the repair options follow from it.

Crown sealing for hairline cracks

Concrete shrinks as it cures, and Technical Note 19B treats that shrinkage as a certainty. The top of a chimney also takes sun and rain on every face while the flue tile grows with each fire, so a crown cast tight against the tile cracks out from the corners of the flue. A mortar wash cracks the same way, only faster.

Cracked chimney crown repair starts with the stage the crack has reached. A sound crown with hairline cracks gets chimney crown sealing, a flexible chimney crown coating brushed over the whole top the way the maker's data sheet sets out: a clean, dry, sound surface, the larger cracks filled first and no rain due before it sets. Tape goes a short way up the flue tile so the coating ends in a clean line, and the joint at the base of the tile stays a flexible sealant joint.

Chimney crown rebuild and replacement

Loose pieces, cracks wide enough to take a coin, a feathered wash breaking up at the edges, or soaked brick under the slab all point to a chimney crown rebuild. We take the old top down to sound masonry, relay any failed top courses and form the new crown with a slope away from the flue, an overhang past each face and a drip groove underneath. Reinforcement goes in against shrinkage and heat cracking, with extra in the overhang, and a bond break separates the new concrete from the brick and from the flue tile.

On a mortar wash that has cracked this far, this is the mortar crown repair we propose, and chimney crown replacement is the same work whatever the old top was. Where a crown cannot overhang, Technical Note 19B shows the last two brick courses corbeled out to form the drip, and it calls for the flue liner to stand at least 2 inches above the crown.

Curing, the cap and the rest of the roof visit

Concrete gains strength slowly, so the pour is booked on a dry forecast, the new crown stays covered and damp while it sets, and the open flue is protected while the forms are up. The chimney cap goes back on once the concrete can hold its fasteners, and a coating on new concrete waits for the time its maker gives.

While we are up top we check the cap's fastening, the top courses of brick and the flashing line below, and brick work or a cracked flue tile gets a separate price. Factory-built chimneys have no masonry crown, since their top is a metal chase cover.

For a masonry chimney crown, call (904) 920-5495 and book a free inspection.