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How to Stop Chimney Water Leaks

The concrete crowns of masonry chimneys often crack with age, allowing water to leak in. This article explains how the crown works, what it should look like and what to do about leaking problems.

By the DIY experts of The Family Handyman Magazine

Understanding chimney leaks

The crown of a masonry chimney is a concrete top that ideally looks something like the one shown. It has an angled top to shed water and it overhangs the brick to keep drips off the chimney sides. It surrounds the clay flues but doesn't encase them. A 1/4-in. gap allows the clay flues to expand and contract from repeated heating and cooling without cracking (or cracking the crown). (The flues “float” inside the brick chimney walls; that is, they're supported by the brick but not attached to it.) A high-quality polyurethane caulk seals the flue/crown gap and prevents water penetration.

In truth, few chimneys built before the mid-1980s have crowns built this well. Many early crowns were simply sloped washes of leftover mortar. Most have cracked and deteriorated, opening gaps around the flues. If you feel safe and confident about walking on your roof, climb up and inspect the crown. If it's sound, caulk cracks and gaps with polyurethane. Otherwise, hire a chimney builder (search online or for “Chimney Builders and Repair” in your yellow pages) or a chimney sweep (“Chimney Cleaning”) certified by the Chimney Safety Institute to evaluate the condition of your chimney and fix it. Flue caps will help reduce water coming down the flue itself, but they won't help much if you have a bad crown.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

    • Caulk gun

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

    • Polyurethane caulk

Comments from DIY Community Members

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January 04, 12:01 PM [GMT -5]

I'm going through a fix of this right now. I had to hire a mason to completely rebuild the chimney below this because the home's original cap was done so poorly. An expanded article on the maintenance required for these caps would be good and what should a homeowner look for when a new one is being installed.

The mason working on my chimney hasn't once noted rebar. He has said he will use portland cement mixed with sand and fine gravel. He doesn't plan to use concrete. Am I not getting what I need? At least he badmouthed the people just using brick mortar for caps.

September 19, 10:41 PM [GMT -5]

I was expecting more of a tip related to the actual repair of a chimney crown, not a caulk job.

September 19, 6:45 PM [GMT -5]

"How to Stop Chimney Water Leaks-- Caulk 'em up or hire a pro."

WOW, that's really helpful FH, a real stroke of genius! How would we ever live without your expert advice!!

Thanks for another brilliant waste of pixels.

:(

September 14, 7:18 PM [GMT -5]

The bricks themselves are like sponges, soaking up water. They must be sealed as well.

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