Expansion Joints Around the Top Flue Tile

Expansion Joints

An expansion joint around the top flue tile serves a very practical purpose. As the fire burns in the fireplace, the hot gases of combustion vent up the flue system. These hot gases, in turn, warm the flue system, causing it to expand. If the crown is constructed such that the cement is installed all the way up to the top flue tile, as the top flue tile expands when it heats, it will crack the crown itself which can cause water problems or other problems to occur.July14 two chimneys 044 (2)

An expansion joint is created by leaving a gap between the actual cement crown and the top flue tile. Then we fill it with a flexible chimney crown, even when constructed professionally, are often installed incorrectly. Everyone has a different philosophy on the proper construction of a chimney crown from the material that should be used to construct the crown to its whether the crown should hang over the edge of the actual brick on the chimney or stay flush. One fact that cannot be disputed, however, is the need for an expansion joint around the top flue tile. A chimney crown lacking an expansion joint around the top flue tile will almost always need to be repaired after some time.

Flexible Sealant

chimney expansion joints
The white ring around these top flue tiles indicates that an expansion joint exists. Cracking is due to the expansion of the top flue tile is not likely.

This flexible sealant allows the flue tile to expand without pushing against the cement crown, preventing cracking. The flue is most likely to expand and crack the cement in the winter time when it is very cold. This is because the cold cement is even more prone to cracking. It cracks from pressure exerted on it by the flue tile.

Crowns constructed without an expansion joint around the top flue tile usually need to be reconstructed entirely.

Although filling the cracks in the crown is an option, the problem is likely to occur again because the same processes are occurring that caused the cracking in the first place. If your crown is cracking and you do not see an expansion joint around the top flue tile, consult a professional. They will be able to assess the situation. Sometimes the cracking is minimal and the professional is able to seal the cracks. They use a high-grade sealant and waterproof the crown. This is in order to prevent water damage from deepening the existing cracks. Other times the cracking has become so severe that crown reconstruction becomes necessary.…. Now I’m starting to sound like a dentist 🙁

I hope that this information helps! Check out our YouTube Videos or our Blogs to learn more about expansion joints and more!
Burn Safe and Warm,

Clay Lamb



Clay Lamb
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6 thoughts on “Expansion Joints Around the Top Flue Tile

  1. Hello

    what foam material is that expansion joint made of and where can I buy some.

    Thank you

  2. Any big box store would have material like this. Its basically a foam roll that you’re going to tape onto the flue tile or your crown and pull and carve the foam material out and then fill it with a high quality silicone. This will allow the flue tile to expand as it heats up, not cracking the chimney crown. Hope it helps. Color doesn’t make any difference. You’re just looking for a foam material. It should be the thickness and the height of the chimney crown, a little more is better than a little less.

    Regards, hope it helps.

  3. Hey clay can’t thank ya enough on the information about the expansion joint at the crown I’m a pretty heavy diyer an I need to replace the crown on my chimney an now I know about the top flu expansion joint much appreciated one more thing is every crown I’ve ever seen mustn’t have had that done to it because they all have been cracked

  4. You got it, every code authority body and building codebook that I have seen requires an expansion joint, for just that reason
    Be very safe up on that rooftop!

  5. Clay! What’s up man hope you are doing well.

    Can I just use sil seal around the flue? The flue won’t get hot enough to melt it?

    Also, what sealant/caulk do you prefer? Thanks man!

  6. We carve out the insulation material that we used to space the new concrete to the chimney flue tile, then fill in the top with silicone

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