The Best Caulk for Chimney Flashing
If your chimney is leaking smoke, soot, and other undesirable substances, you need to seal the joint between the chimney and the roof (also known as the chimney flashing). Over time, that joint can develop cracks and gaps that let in moisture, which can lead to rust and rotting.
Fortunately, caulking is an easy fix—once you figure out which type of caulk to use. We spent six hours researching and testing 10 different caulks, and we chose these that are specifically formulated for chimney flashing.
| # | Name | Preview | Rating | Action |
| 1 | Dap Inc 18152 6 Pack 10.1 oz. Alex Plus Acrylic Latex Caulk Plus |  | 9.7 | |
| 2 | Gorilla Waterproof Caulk & Seal 100% Silicone Sealant, 10oz Cartr |  | 9.4 | |
| 3 | Red Devil 0405 Duraguard Kitchen & Bath Siliconized Acrylic Caulk |  | 9.3 | |
| 4 | Gorilla Waterproof Caulk & Seal 100% Silicone Sealant, 10oz Cartr |  | 7.8 |
Our Methodology for Testing
To test each caulk, we installed a 3-inch-wide section of caulk between a steel chimney flashing and the top of a brick chimney. We then subjected each caulk to two tests: one for adhesion, and one for flexibility.
After each test, we measured the height of the caulk remaining on the chimney to see how well each caulk held up over time.
We measured adhesion in two ways: first, we tried to pull the caulk out of its application; second, we used a utility knife to try to cut the caulk horizontally along the face of the chimney.
As for flexibility, we installed the caulks on a cold day (around 35 degrees Fahrenheit), then tried to flex them. We also checked to see if any of the caulk cracked when we flexed it.
To make sure that any dust or debris didn’t affect our results, we ran each test a total of four times (two times for each test).
Dap Inc 18152 6 Pack 10.1 oz. Alex Plus Acrylic Latex Caulk Plus
Things That Make It a Good Investment
The Dap Alex Plus Caulk (which also comes in an Ombre Color option) is a great all-purpose caulk that’s tough, flexible, and paintable. In our tests, it shrank less than other types of caulk, making it easier to apply, and it was the only caulk we tested that was fully paintable with latex or oil-based paints in just 30 minutes.
It should never shine through or discolor paint finishes, and the cured caulk is mold and mildew resistant. It’s also easier to apply and tool than other types of caulk, and it smells less. The Alex Plus is a good choice for most construction and maintenance projects, including kitchen and bath remodels, siding, roofing, and even the exterior of a hot tub or swimming pool.
Gorilla Waterproof Caulk & Seal 100% Silicone Sealant, 10oz Cartr
Things That Make It a Good Investment
The Gorilla Glue 100% Silicone Sealant is easy to use and produces a strong, permanent seal in as little as 30 minutes. Unlike most clear caulks, it comes in an indoor/outdoor cartridge that’s water-ready right away, so you don’t have to let it sit for hours before using it.
This caulk is 100% waterproof and should never crack or yellow over time. It’s also available in clear and white variations.
While we prefer Gorilla Glue’s clear caulk for sealing windows, because it’s the only clear caulk we’ve found that’s actually clear, the brand’s white is also a good choice if you prefer an opaque white finish.
Red Devil 0405 Duraguard Kitchen & Bath Siliconized Acrylic Caulk
Things That Make It a Good Investment
The Red Devil 0405 Duraguard Kitchen & Bath Siliconized Acrylic Caulk is the best choice for a variety of surfaces and applications.
It offers the best performance in our tests for adhesion, and it’s still easy to work with even if you don’t have specialized tools. It also comes in a large size that’s easy to use, even for people with larger hands.
Most DIYers should be able to get a professional-looking repair with this caulk. It also offers good resistance to discoloration, and it cleans up easily with soap and water.
Gorilla Waterproof Caulk & Seal 100% Silicone Sealant, 10oz Cartr
Things That Make It a Good Investment
The Gorilla Waterproof Caulk and Seal 100% Silicone Sealant (in either white or clear) was the toughest of the caulks we tested. It withstood being dunked in cold water for 30 minutes without developing a soft and potentially messy edge, as most other caulk did.
It also resisted high temperatures from the heat of a hair dryer and didn’t melt when we coated it with a heat gun.
This caulk is 100% waterproof, making it an excellent choice for bath and kitchen projects like sealing a sink or a tub as well as a fireplace or a foundation. It should never yellow, shrink, or crack. Our testers found the clear caulk easier to apply than the white, which can be a little more difficult to work with.
Some Factors That Shouldn’t Be Overlooked
We considered the following factors while researching and testing caulk for chimney flashing:
Adhesion to Masonry
A good masonry sealant should be able to adhere to a wide range of brick types and mortar joints, as well as stone that’s exposed to the elements.
Caulk should also stick to concrete or stucco in a chimney or fireplace, which is often covered with a thin layer of cement stucco.
In our testing, we looked for sealants that were easy to apply in corners and on curved surfaces.
All of the products we tested are rated for use on masonry, but some performed better than others.
Drying Time
The best sealants will dry quickly enough so that you can grout within a day or two. We looked specifically for products that could be applied during warm months without significantly delaying project schedules.
Frequently Asked Questions
What type of caulk is best for chimney flashing?
The best type of caulk for chimney flashing is silicone caulk. Silicone caulk is waterproof, flexible, and resistant to extreme temperatures, making it the ideal choice for chimney flashing.
Does the caulk need to be UV-resistant?
It depends on the type of caulk you are using. If you are using a caulk that is designed for outdoor use, then it should be UV-resistant. However, if you are using a caulk for indoor use, then UV-resistance is not necessary. Also, if you’re searching for a caulk to install on your roof, use the best caulk for metal roof instead.
Are there any specific application techniques for chimney flashing?
Yes, there are some specific application techniques for chimney flashing. These techniques include installing a drip edge, properly sealing the joints between the flashing and the chimney, installing a counter flashing, and properly caulking the joints between the counter flashing and the chimney.
Also, it is important to make sure that the flashing is installed correctly and that it is securely fastened to the chimney structure.
How long does the caulk need to last?
The length of time that caulk needs to last depends on the type of caulk and the conditions it is exposed to. Generally, most caulks are designed to last between 5 and 10 years, but can last much longer if the conditions are favorable.
Is there a specific type of caulk that works better for chimney flashing than others?
Yes, there is a specific type of caulk that works better for chimney flashing than others. It is called high-temperature silicone caulk, or heat-resistant caulk.
This caulk is designed to withstand high temperatures, so it won’t break down over time as regular silicone caulk would. It also forms a flexible seal that can expand and contract with temperature changes.
