How to Fix a Leaky Chimney


If you are having leaking problems and can't seem to find the problem, consider looking at your chimney with more scrutiny. Often a chimney can leak profusely, and can bring a lot of water into the interior of your home. Along with water comes other problems such as black mold or mildew gaining access to your home. Mold loves to grow in dark and damp areas. A leaking chimney can also result in structural damage. Regardless of what problem you may or may not have, finding the leak and repairing it are of the utmost importance.

Things You'll Need

  • New chimney cap material or flashing
  • Copper roof flashing
  • Masonry waterproofing
  • Low pressure garden sprayer
  • Check all areas around your chimney, both inside the home and outside. Water infiltration will be more obvious in the interior of the chimney as you will see stained bricks with drip marks, or loose and swollen drywall. Other materials will exhibit similar problems so look carefully. Get up on the roof and give the chimney careful examination. The biggest culprit can be the chimney cap. If it is poured concrete or cast stone or natural stone, check for cracks, caulking problems or a dislodged cap.

  • Check for missing mortar, cracks in the mortar or spalled brick, which means the faces of the brick have frozen off due to moisture penetration. Also, inspect the flashing where the brick joins the roof. Check the flashing to see that it is not loose or hanging off the brick and that it is properly secured to the roof and covered with shingles.

  • Cracks in the chimney cap, will give you 2 options. First you can remove and replace the cap with new materials. Coat the top surface of the cap with a commercial clear waterproofing agent. This will soak into and seal the cracks. The second option is to have a copper cap fabricated to fit over the existing cap. It is best to first coat the existing cap with a sheet-applied membrane waterproofing, covering all exposed surfaces. The copper serves to protect the membrane.

  • Coat all exposed masonry surfaces on a masonry chimney with a clear masonry waterproofing sealer. This is applied in 2 separate coats with a garden sprayer set on low pressure and let the waterproofing run down the brick to assure adequate material is being installed. Let dry and re-apply. Brick supply vendors have the highest quality masonry waterproofing sealer.

  • Nail, tar and caulk the flashing back into place if it has come loose. Many chimney leaks are the result of flashing that has peeled up or the sealant undercoating has deteriorated.

Tips & Warnings

  • If in doubt with anything you see, be sure to get the opinion of a qualified roofer and home inspector.

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  • Photo Credit Hemera Technologies/ Images
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