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Why do chimney crowns crack?

April 26, 2017chimney crack crowns

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Posted

Why do chimney crowns crack?

2 Answers

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reid Bandremer Posted

Chimney crowns can, and do, crack for many reasons. As Mr. Roof states, it generally comes down to the cement not being flexible enough to handle the the stresses put on it.

Cracking during the intially curing process is one cause.
Another is the stress from freezing/thawing. When water freezes, it expands – putting pressure on the cement.
Another reason could be the shifting of your structure over time.
If the chimney crown was not installed according to best practices, that could contribute to cracking as well. For example, crowns should be slightly curved on top so that water runs off. Also, crowns should be coated with sealant (Chimney Saver Crown Coat is an example of an appropriate sealant) to seal out water.

For related articles, see #2 in http://www.highschimney.com/articles/reasons-chimney-leaks and http://www.highschimney.com/articles/all-about-chimney-crowns/

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Posted

• Cement is not very flexible. Expansion and contraction of the masonry is one reason for cracking. As well, like a cement sidewalk, very small cracks often develop during initial curing. Small cracks become large cracks over time.