Whenever it rains, the ceiling becomes wet at the corner of the chimney.

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I ASSUME it's just a small leak, but obviously I don't want it to become any worse. I have a flat roof, so getting up there and doing some work is pretty easy for me. Any suggestions on what I need to do? My Googlefu has come up with this plan of attack:

  1. Repair and cracks I find in the morter with masonry sealant.
  2. Spray the chimney with water repellent.
  3. Caulk where flashing meets the chimney with flashing sealant.
  • I would inspect the flashing where the roof meets the chimney. That would be my first guess where the leak is coming from. Nov 5, 2015 at 15:18
  • Can you access the attic?
    – dotjoe
    Apr 13, 2016 at 20:25

2 Answers 2


98% of small leaks are water getting into the flashing area between the chimney and the flashing or the flashing and the shingles.

The flashing sealant you have should work fine - although you need to make sure for a caulking type sealant that this is applied liberally and squeezed into the gaps. I often use FlexSeal for smaller leaks because of its expanding properties.

If you post a picture of your chimney I can highlight where you need to seal.


I had a similar problem. A rental house I maintain had a low pitched gravel roof that would leak around the chimney as soon as it rained. I looked at the obvious sections were water might penetrate around the chimney: flashing, brick mortar, the mortar cap on the brick, etc.. And used a few gallons of roof patch applied everyplace in the vicinity of chimney. Still leaked with no sign of slowing down. Pausing to think what I was missing and leaning on the chimney my eye caught the slightest sign of a hairline crack running on the inside of the flue vertically for about 10 inches. Peering more closely I could see the rain had ran down the inside wall of the chimney all around the break. Running out of possible entry points I chiseled to widen the crack, wire brushed the dust out, and troweled in cement patch. The tenant hasn't called about the roof leaking since. Conclusion: roof leaks aren't always in the roof.

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