Over the past thirty years, I have seen and estimated thousands of chimneys that were damaged due to poor design or being constructed of the wrong materials. Customers will often ask me what is the best chimney crown repair for their money if their service
professional has come out and cited damage to the chimney’s crown. The chimney crown is often incorrectly referred to as a cap by customers, and the purpose of the crown is to shed water off the top of the brick chimney chase and to cap off the brickwork of the chimney.
Freeze-thaw damage is the most frequent type of damage I see to chimney crowns is. If your chimney is saturated with a cold rain and the temperature drops well below freezing, freeze/thaw damage occurs. On-going freeze-thaw cycles will not only cause cracks and other damage to the chimney’s crown, but can cause a chimney to experience premature brick spalling. Spalling is characterized by the brick faces popping off. You may see them lying on the rooftop or on the ground near the area where the brick has become damaged.
Customers are often confused as to why the brickwork on the top of the chimney near the chimney crown is damaged when the rest of the brick on the home seems fine. Well, if you stop and think about it, most of the bricks on a home are pretty well protected by the overhanging eaves and gutters, but the chimney sticks up on the side or very top of the house where it is exposed to the strongest winds and coldest temperatures.
In a nut shell here is the real problem surrounding why chimney crowns need repaired. Your chimney crown is supposed to be constructed of concrete mix and not brick mortar mix. A properly constructed crown will also have a membrane under the concrete that 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 supposed to have an expansion joint around it so that the flue tiles can expand when the fireplace or appliances that they are venting heat up without pushing on the crown causing it to crack.
Most building codes do not require an overhang or what is sometimes referred to as a drip edge crown, but it is definitely suggested to keep the water shedding off of the sides of the chimney. Many bricklayers adopted the attitude of their building superintendents to “hurry up and get the job done”. It is quite obvious today that they were all getting paid for production, not their craftsmanship. At the end of the day, when all of the bricks had been laid, if the bricklayer had enough mortar mix on the board they wouldn’t climb down the scaffolding and mix up the proper concrete material to finish the crown. This is the ugly truth of chimney crowns, especially those on older homes when houses were being built very rapidly.
All in all, I would discuss the options that your chimney repair man has cited as possible and also call out for a second or third opinion. Sometimes the chimney crown can be resurfaced and other times the crown needs to be removed and replaced with the correct materials. In severe cases where the chimney has not only incurred damage to the crown but also to the brick on the top of the chimney, the top portion of the chimney may need to be rebuilt.