Customers often ask what’s the best crown repair after getting the confirmation of chimney crown damage. Remember, the chimney crown is not a cap. The purpose of the crown is to shed water off the top of the brick chimney chase. Its also to cap off the brickwork of the chimney.
Freeze-Thaw:
Freeze-thaw damage is the most frequent type of damage I see to chimney crowns is. If your chimney is saturates with cold rain and the temperature drops well below freezing, freeze/thaw damage occurs. Ongoing freeze-thaw cycles will not only cause cracks but can cause premature brick spalling. Spalling is the brick faces popping off. You may see them lying on the rooftop or on the ground near where the brick is breaking.
Customers don’t understand why the brickwork near the crown is damaging when the rest of the brick seems fine. Well, if you stop and think about it: most bricks on a home are get protection by overhanging leaves and gutters. The chimney sticks up on the side or very top of the house. This exposes it to winds and the coldest temperatures.
In a nutshell here is the real problem surrounding why chimney crowns need to be repaired. Your chimney crown construction should be of concrete mix and not brick mortar mix. A properly constructed crown will have a membrane under the concrete. This separates it from the top of brick chase. The concrete mix itself should have wire mesh or reinforcing fiber incorporated into it to further strengthen the crown. Chimney flue tiles will stick out of the top of the chimney, and each flue tile is to have an expansion joint around it so that the flue tiles expand when the fireplace or appliances they are venting heat up without pushing on the crown causing it to crack.