Caulking or silicone spray will not seal a chimney
A proper chimney seal is crucial for any flat roof. Mortar cracks, chimney flashing and crown deterioration on a chimney will contribute to leaks on a flat roof. All chimneys need maintenance over time. The mortar grout is usually the first to go. Re-pointing a chimney is not a simple process and is often messed up by novice people that try to do it. Some try to use caulking or some spray sealant like silicone.
Watch this video to see how to seal cracks on a chimney.
Depending on the situation and type of chimney, there are different ways to seal a chimney. Before making repairs, it is necessary to find out what is exactly causing the leak. Watch the various videos to see where and what to look for on a chimney and how to go about to seal it.
Watch this video on how to wrap an entire chimney with a rubber membrane sealing it.
When a chimney does not have to be aesthetically pleasing, then wrapping it with a rubber membrane will be the most inexpensive way to seal it. There are not many roofing contractors that will offer such a service, but anyone that knows how to do a torch down roofing system should be able to do it.
The Chimney Crown
The most common part of a chimney that causes leaks is in between the cement slab and the body. Most cement slabs (crown) are too thinly poured. The edge of the slab will often separate from the bricks and water will easily flow into the crack. There are two ways to solve this problem.
- Remove the old cement slab and pour a new thicker slab
- Install a Modified Bitumen Rubber Membrane over the existing slab
Before we wrapped a chimney in NY.
This was a chimney in Manhattan NY. Although it was stuccoed, there were cracks and causing leaks. This was a challenging project because it was five stories high and there were people below on the sidewalk.
A close-up look at cracks in the chimney
Notice the tar that has peeled off. Many attempts to seal the chimney over the years have failed. Tar is a very temporary seal on a chimney. The stucco is cracked.
Chimney sealed with a rubber membrane
This is what the chimney looked like after we sealed it with a rubber membrane. Because the chimney is located on the 5th story in Manhattan, the appearance did not matter that much.
This stucco chimney needs maintenance. When a chimney gets neglected like this one, then it will cause a roof leak.
So often it’s the chimneys that cause leak issues on a roof. Any chimney whether it be a fieldstone or brick chimney needs maintenance over time. Most of the time it’s ignored and left to a roofer or maintenance person to make the necessary repairs.
Most commonly someone will caulk the flashing or smear tar over the flashing and the bricks. Regardless of how it’s fixed, the problem just gets worse over time.
When we see a chimney leak like this one in the video, we recommend to wrap it with a rubber membrane. It’s less expensive and will not need any maintenance for the next 20 years.
Videos are taken from my iPhone.
Fieldstone chimneys are the hardest to fix or seal against water. So often we see that the water would get through small cracks in the stone itself rather than the grout. What makes stone chimneys so hard to seal is the grouting or pointing. When a mason builds a stone chimney, he is more concerned about the aesthetics or looks than the water tightness.
What happens is they use as little mortar as possible in the grout lines to avoid getting the stone covered with cement. It is a battle to grout between the stones and keeping the stone face clear of getting messy with the cement. Several years after the chimney was built, the cement grout starts to deteriorate and causes cracks that let water in.
The crown is a small cement slab on the top of the chimney. Most of the time that is what starts the leaky problem.
The beginning of the chimney leak battle.
After a leak has developed in a chimney, the normal thing to do is seal the crack. People will use any product for that purpose. Silicone caulk is the favorite one. We have seen all kind of caulking products to tar. The end result is the chimney leak just got worse.
Caulking on cement, brick, and stone does not work to good. More often than not the water gets into the bricks and stone from cracks that are barely visible to the naked eye. Caulking the cracks you can see does not always seal the leak.
Removing the grout between the stone and then re-point the chimney with new cement is the best way to fix the leaky problem.
We have found that removing the old cement grout and replace with new is the best solution. we also cover the top of the chimney crown with a rubber membrane. That way we are guaranteed that the water can not seep in from the top.