Spray rubber sealants like Flex Seal can stop a small roof leak for a while on a clean, dry surface, and they are handy for an emergency patch. They are not a lasting roof repair. They do not replace a cracked pipe boot, failed flashing or missing shingles, and in strong sun they wear down. Use them to get through a storm, then fix the part that failed.
Where spray sealants help
- A small crack or hole on a metal roof, gutter or flashing
- Around a vent collar as a short-term patch
- Small spots on mobile home roofs between proper coatings
- Patching a drip before a repair can be scheduled
Where they fall short
- Spraying over a chimney or wall joint instead of fixing the flashing
- Spraying over curled, cracked or missing shingles
- Coating a whole roof with a spray can
- Using it on a wet or dirty surface
- Spraying over granules that later wash off, taking the coating with them
Why it does not last on shingles
Asphalt shingles shed water because each row overlaps the one below. Spraying rubber over the joints can trap water under the shingles instead of letting it drain. The coating also sticks to loose granules, not the shingle itself, so it peels. And spraying over the seal strips can make it harder to replace those shingles later.
A better choice for large areas
For flat, metal or mobile home roofs, a proper elastomeric roof coating, applied after cleaning and sealing seams, lasts much longer than spray cans. See roof sealing and coating and mobile home roof leak repair.
How to use a spray sealant as a temporary patch
- Only on a dry day, and only on a roof you can reach safely.
- Clean the area with a brush. Let it dry completely.
- Spray several light coats past the edges of the damage, letting each dry.
- Check it after the next rain and plan a proper repair.
The honest bottom line
A can of spray sealant is a good thing to have in the garage for a leaking gutter seam or a pinhole in metal. It is not a replacement for a roofer finding where the water gets in and fixing it. We find a lot of leaks under old sprayed patches that were never fixed underneath. See is caulk a permanent roof fix and roof leak detection.
Will it void my shingle warranty?
It can. Many shingle makers only cover their products when they are installed and repaired to their instructions. Coatings sprayed over shingles may not meet those instructions. Check your paperwork before coating a newer roof.
How long do spray patches last?
It depends on the sun, the surface and how well it was prepared. On a clean metal surface in partial shade, a patch may hold for a year or more. On shingles in full sun, it often starts peeling within a season.
Should I spray the inside of my roof?
No. Spraying the underside of the decking from the attic does not stop water coming in from above. It can trap moisture in the wood and hide where the leak is.
Can Flex Seal fix a leaking roof permanently?
No. It can stop a small leak for a while. The failed part still needs a proper repair.
Does spray sealant work on shingles?
Not well. It sticks to loose granules and can trap water under the shingles.
Is spray sealant good for metal roofs?
It can patch pinholes and small gaps for a while. Leaking screws need new screws.
Can I spray it on a wet roof?
It sticks far better to a clean, dry surface. Wait for dry weather when you can.