How to Seal a Leaking Brick Chimney

Lead Image
  • 4-8 hours
  • Beginner
  • 20-200-
What You'll Need
Hose and sprayer (optional)
Sealant for chimney flashing
Caulking gun
Crowbar or screwdriver
Replacement bricks

Leaks in a brick chimney can be dangerous for your home. Leaks allow moisture into your home which can Sealing leaks in a brick chimney can be a lot of hard work but can save you a lot of time and hassle in the future if you seal the leak before it causes too much damage. Here are the steps you will need to take to seal a leak in your brick chimney.

Step #1: Find the Leak

If you live in the Northwest or other similarly rainy location, finding a leak in your brick chimney is easy. After a rainstorm, climb to your roof and look down into your brick chimney with a flashlight. Look for holes or other places in the brick chimney where water has leaked through the bricks, especially in the flashing between where the chimney meets the roof.

If you're not quite so lucky, and rain doesn't fall quite so often in your location, you'll have to provide your own. Drag your hose up to the roof and spray water on your brick chimney, especially in the flashing. After you're done, look down the chimney with your flashlight as described above.

The two biggest locations where you will find a leak occurs in one of two places. The leak could be in the flashing or could be in the brick or mortar. What you do next depends on where the leak in the brick chimney occurs.

Step #2: If Your Leak is in the Flashing

Leaks occur in places where sealant in the brick chimney flashing has become broken or damaged. Before applying the new sealant to fix the leak in your brick chimney, you'll need to scrape out the previous sealant using a scraper.

Apply sealant to the flashing of your brick chimney using a caulking gun. The area that needs attention is where the chimney meets the roof. Let the sealant dry after application, and unless you purchased a sealant meant for wet weather, avoid getting it wet during the drying process.

Once the sealant is dry, apply a second layer over the first.

Step #3: If Your Leak is in Brick of Mortar

Bricks and mortar can become damaged letting in moisture and causing leaks. Sealing these leaks are a little more involved than just applying sealant.

First, the damaged pieces of brick and mortar need to be removed. You can do this by prying apart the pieces with a crowbar or screwdriver. Use the caulking gun to apply mortar and replace any bricks that were removed.

Finally, coat the entire outside of your brick chimney with waterproofing to help prevent future leaks.

Remember, it's important for your safety and the health of your house to fix any leaks in your brick chimney as soon as they're discovered.