Chimney Crowns Done Right

Cracked Chimney Crown
This chimney crown is not smooth and will allow water to sit, causing cracks. Note the use of foam around the top flue tiles to provide for an expansion joint, required in many areas.

Chimney crowns are very important to the integrity of your chimney; an improperly installed chimney crown could cost you thousands of dollars in repair work down the road. Using the right materials, following the correct procedure, and consulting with a professional will help you to construct a chimney crown properly. The chimney crown helps to prevent the mortar in between the bricks on your chimney from eroding away in rainfalls.

Removing your existing chimney crown is often where mistakes occur. You do not want to damage the brick on the chimney or the chimney flue itself. To prevent incidental damage from occurring, chisel off the existing crown starting from the edges and working your way in. Work carefully and wear eye and hand protection to protect yourself from flying bits of concrete.Similarly, remember that you are working likely on a roof or a ladder and are up in the air. Follow all building codes in your area and never do anything that you do not feel comfortable doing; this may lead to injury.

Chimney Crown Repair
An air pocket may have existed when this chimney crown was poured which allowed water to cause damage.

We never recommend using mortar to construct your crown. Mortar is very vulnerable and will erode away quickly. Cement crowns will outlive crowns constructed from mortar every time. Making a consistent and appropriate concrete mixture is important to having a crown that will not easily be damaged by water or freezing and thawing. Although you should follow the directions on the cement that you buy exactly, usually you must mix all of the dry ingredients prior to adding any water. Be aware that when applying the cement to the chimney, air pockets inside the cement will prevent it from standing as strong as possible.

You are going to need to set some steel forms on the chimney to fill up with cement. We recommend installing a 2″ or 3″ drip edge crown, which means the steel forms allow for the chimney crown to be constructed with an extra two or three inches on each side of the chimney. This prevents water from dripped directly down the brick on your chimney. Fill the steel forms up completely with cement to ensure a very flat top. A top that is not completely flat will allow water to pool which will catalyze your chimney crown’s deterioration.

After your chimney crown has had time to cure according to manufacturer’s instructions, waterproofing your chimney is a wise investment. Spending less than fifty dollars to waterproof your chimney crown  will prevent damage in the future that will cost much more to repair. When water is able to sit directly on top of the crown, it will expand and contract as it freezes and thaws and slowly but surely create cracks in the crown. These cracks can be filled by specialized chimney crown repair products, but if the cracks get too deep then often times the crown must be completely replaced. Such a repair can costs thousands if done professionally. Waterproofing your chimney crown prior to such damage is always the best decision.

Clay Lamb
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2 thoughts on “Chimney Crowns Done Right

  1. Isn’t a slightly sloped crown advisable to promote drainage and prevent pooling? What is the proper way to construct the expansion gap between the concrete crown and a terra cotta clay flue?

    I’ve had a couple contractors bid my masonry chase and concrete crown repair. One has proposed installing a stainless steel, factory painted chase cover. The other wants for pour a new concrete crown. I am concerned that the mason who has bid the concrete crown does not intend to construct one with an expansion gap, does not intend to groove the drip-edge, and plans to pour a drip edge that extends only 1 inch beyond the chase. He’s been building them this way for “30 years without a problem”, and blew-off my questions about these items as something “a guy on Youtube says should be done that is unnecessary”. (I didn’t find these recommendations from a guy on Youtube, but from many sources on professional masonry and inspection websites.)

    The other contractor does not want to bother with concrete. Is a steel crown (called a chase cover?) appropriate for a masonry chimney? Both contractors will replace 3 courses of masonry, as the blonde brick is flaking. I’ve been told that blonde brick is softer due to bleaching, and thus is more prone to deterioration secondary to water exposure.

    Finally, the 1971 brick on my home is 0.25 inch longer than the bricks available now. We need to have bricks replaced not only on the crown, but one brick on the corner of each course of the chase, down to the ground, where ice damming has caused water damage along the corner brick. One mason plans to buy larger bricks and cut them down to size (a lot of work!), while the other plans to simply use more mortar. Are both approaches acceptable from the standpoint of integrity?

    Thank you, I appreciate any advice. It seems there are very few chimney masons in Utah who are willing to repair. If you have suggestions on finding contractors, I would appreciate that as well.


  2. Let’s walk this out, first off excellent job on homework. a selection of either mason is possible but I would want to see some of their jobs they’ve completed in the last three to five years. the expansion joint around the flue tile is building code compliant in most communities whereas a drip edge is not. I would think that I would want a drip edge and a groove cut out underneath and an expansion joint, but let’s take this a step further, im starting to see more contractors puttinG stainless steel chase covers over the crown. I think it has a lot to do with the changing ingredients through the years and the aggregate stone being used. also i recommend a fiber hair in the concertre mix when they pour that, it makes it a tighter feel. good job! there’s someone out there would do it right for you.

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