How to Repair a Chimney Crown
Depending on the size and severity of the cracks, you might be able to use products to repair the cap, or you may need to remove the old crown and build a new one.
The mortar crown on my chimney needs repair. There is damaged mortar leaving holes against the flue and also hairline cracks. Can you folks recommend some products to do the repair? From what I have read there are different products used for larger holes vs. hairline cracks.
—Jim Milgroom via the FHB forum
John Carroll, a mason in North Carolina, replies: If the crown is crumbling, has large structural cracks, or has deep dips that hold water, you need to remove the old crown and build a new one. Smaller chips and hairline cracks are typically repairable.
Start by chipping off the small loose pieces near the flue liner, then remove grime and loose material from the surface of the entire crown with a wire brush. Use a stainless-steel brush to avoid future rust stains caused by the steel bristles that break off in the process of scrubbing. If the chips you remove create dips that will hold water, patch them with quick-setting repair mortar, and then seal the cracks with siliconized acrylic latex sealant.
After the patching materials have dried, brush on a water-based elastomeric coating designed for chimney crowns. I’ve had excellent results using Chimney Rx Brushable Crown Repair. And most importantly, don’t take on these repairs yourself if you don’t have the proper equipment and experience to safely work on a roof.
From Fine Homebuilding #311
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