Chimney Crown Repair

The very top of your chimney stack is covered by a flat slab called the **chimney crown**. This crown is like a concrete roof for the chimney, and it’s arguably the most important weather shield your entire system has. Its job is simple: to sit above the bricks, divert rain and snow away from the chimney walls, and prevent water from pouring down the outside of the flue liner. The most important feature of a good crown is an **overhang**, or drip edge, that extends past the brickwork so water drops harmlessly to the roof below instead of running down and soaking the bricks. The vast majority of crowns we see are failing because they were poured incorrectly in the first place. Many builders just use basic mortar mix, which isn't strong enough, or they simply apply a thin layer right up to the flue tile. Basic mortar and a thin layer crack quickly. Cracks usually appear where the crown meets the flue liner (the heat source) and spiderweb across the flat surface. Once a crack is there, water flows right into the chimney structure. This water then seeps down the inside of the brick stack, accelerating mortar failure and brick spalling (popping off the brick face). When the crown fails, water gets funneled into the chimney structure in two critical ways. First, it pours straight into the porous brickwork, leading to freeze/thaw damage. Second, and more dangerously, it runs down the outside of the clay flue tiles. This trapped water saturates the brickwork surrounding the flue, leading to leaks, mold, and eventual structural collapse. Simply put, **a cracked crown guarantees a chimney leak**. Our process for crown repair depends on the severity of the damage. If the crown is completely broken, thin, or improperly sloped, we may need to demo and pour a **brand-new concrete crown**. This involves using specialized formwork to create a proper thickness (at least 4 inches), mixing a high-strength Type-S concrete, and ensuring it has a proper slope to shed water and a full drip edge. We also isolate the concrete from the hot flue liner by installing a **bond breaker** around the tile so that the crown can expand and contract independently, which prevents cracking. However, for a crown that is mostly intact but has developed common shrink cracks, we use a repair product called **CrownSeal**. CrownSeal is a flexible, highly durable elastomeric coating that is specifically engineered for chimney crowns. We first clean the existing crown thoroughly, removing any loose debris, moss, or dirt. Then, we apply a base layer of CrownSeal. We embed a layer of **fiberglass mesh** into this wet coat, which reinforces the repair, similar to how rebar strengthens concrete. Finally, we apply a heavy top coat of CrownSeal over the mesh. The finished CrownSeal repair is not only perfectly watertight but is also flexible. This flexibility is key, as it allows the crown to handle the expansion and contraction from the chimney’s heat cycle and the varying Suffolk County temperatures without cracking. Unlike patching with regular mortar, which will crack again almost immediately, the CrownSeal membrane moves with the chimney. It eliminates leaks and restores the essential drip edge function that protects the bricks below. This repair is robust, typically comes with a 10-year warranty against water penetration, and is significantly faster and less invasive than a full concrete demo and pour. It's the most reliable way to secure the very top of your chimney and prevent future water damage from the top down.