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RV sealant can look fine when you apply it and still fail once it has to stretch, stay bonded, and survive months outside.
Two RV-focused YouTube channels recently put popular sealants to the test. Some products performed very well. Others cracked, peeled, or broke apart much sooner than expected.
The tests also showed why choosing one sealant for every part of an RV may not be the best approach.
An RV technician tested popular exterior sealants
In his comparison, That RV Tech tested a dozen sealants that could potentially be used around exterior RV seams, trim, and components.
The lineup included Sikaflex 221, Sashco Through the Roof, Lexel Clear, Big Stretch, Vulkem Max, OSI Quad Max, Geocel Pro Flex RV, DAP Ultra Clear, DAP Dynaflex Ultra, Loctite Polyseamseal, Flex Glue, and 3M Fast Cure 4000 UV.
He focused on three areas: flexibility, adhesion, and ease of use. Each sample was allowed to cure for more than two weeks before testing.
Flexibility was a major part of the comparison because an RV body moves. Seams are exposed to vibration, expansion, and contraction as temperatures change, so a sealant needs to move without separating or breaking.
Several products struggled almost immediately.
Some sealants broke apart during the stretch test
Flex Glue was one of the first products to fall behind.
According to That RV Tech’s test, it cured relatively stiff and eventually snapped apart when stretched.
Geocel Pro Flex RV also performed poorly in the stretch test. The result surprised him enough that he applied another bead, allowed it to cure, and tested it again. He reported essentially the same result, with the material pulling apart before several competing products did.
DAP Dynaflex Ultra and Loctite Polyseamseal were also among the weaker performers when stretched.
Other sealants behaved very differently. Products such as Through the Roof and Lexel could stretch a long distance, while several hybrid sealants had a firmer, spring-like quality and returned toward their original shape.
Stretch alone was only part of the test.
The strongest adhesion created another problem
Sikaflex 221 had the strongest adhesion in the fiberglass test.
It was so firmly attached that removing a short section became difficult. The plastic scraper often cut through the sealant rather than cleanly separating it from the fiberglass.
3M Fast Cure 4000 UV was another standout for adhesion and was also difficult to remove.
That strength can be useful, but RV components eventually need service. Water heaters, exterior lights, furnaces, windows, and other parts sometimes have to come back out. Extremely aggressive sealants can make that work more difficult.
After considering flexibility, adhesion and ease of application, That RV Tech’s top performers were OSI Quad Max, Vulkem Max and 3M Fast Cure 4000 UV. He also included Sikaflex 221 among his finalists for applications where its strong adhesion made sense.
If he had to choose one overall, he picked OSI Quad Max, partly because it performed well across the tests and is widely available.
That test covered general exterior sealing, but RV roofs often have their own requirements. Many roof seams and penetrations use self-leveling sealants designed to flow across horizontal surfaces and remain compatible with the roof membrane. That is where the second test from All About RVs comes in.
A second test focused specifically on RV roof sealants
Jared Gillis of All About RVs tested products designed for sealing roof penetrations and horizontal seams.
His test included Dicor, Extreme Ply, two Alpha sealants, two Forever Lap formulations, Liquid Rubber, GoClean, EternaBond tape, Flex Paste, and Sikaflex.
Rather than stopping after the sealants cured, Gillis left the test panel outdoors to see how the products changed with exposure to sun, rain, dirt, and seasonal weather.
When he returned to inspect the samples, two failures stood out.
Flex Paste had cracked and lost part of the material. Gillis found water underneath it extending to the fixture he was trying to protect. He considered that a complete failure and ruled it out for his roof.
GoClean also performed poorly. Gillis had seen adhesion problems during his earlier testing, and months later parts of the sealant could be peeled away while he cleaned the panel.
Other products held up considerably better.
Dicor was still firmly attached
Dicor looked good when Gillis inspected it after the outdoor exposure.
It cleaned up well, and he could not easily lift the edges from the roofing material. He did notice some early surface texture that he planned to watch, based on his previous experience with Dicor drying and cracking as it ages.
The original Forever Lap sealant also performed well. It cleaned up and remained firmly bonded to the roofing, plastic, and metal used in the test.
The extra-leveling version of Forever Lap was easier to lift from the new roof sample in places. That result led Gillis to uncover a limitation with his test setup.
New and older RV roofs produced different results
The test panel used new roofing material.
Gillis had also applied one of the sealants to the older roof on his actual RV. When he checked that application, the bond was much stronger. He could not get underneath the edge, and the sealant remained firmly attached.
That suggested the age and condition of the roof membrane could affect adhesion.
Gillis acknowledged the limitation and said he was aging additional roofing samples for future testing.
It also changed how he would approach sealing a new RV.
His choice depended on the age of the roof
After reviewing the weathered samples and the sealant on his own RV, Gillis said he plans to use Forever Lap sealant on his roof for now.
His recommendation for a brand-new RV was different.
For roughly the first six to eight months, he said he would probably use Dicor because it bonded so well to the new roofing material in his test. After the roof had aged, he would move toward Forever Lap.
He particularly liked Forever Lap’s combination of adhesion, flexibility, and ability to stretch.
Gillis also cautioned owners to consider their RV and roof manufacturer’s requirements, especially while the RV is under warranty.
There wasn’t one winner for every sealing job
Taken together, the tests show why sealant choice depends on the specific application.
That RV Tech’s broader exterior-sealant test favored several modern hybrid products, with OSI Quad Max becoming his overall choice. However, OSI’s technical documentation says Quad Max should not be used for roof applications, so it should not be treated as a replacement for a self-leveling RV roof sealant.
In the roof-specific test, All About RVs found strong results from both Dicor and Forever Lap, with the age of the roofing material affecting which product Gillis preferred.
The failures may be just as useful.
Flex Glue struggled with stretching in That RV Tech’s test, while Flex Paste cracked and allowed water underneath it during the All About RVs weathering test. Several other products showed adhesion or flexibility problems that became obvious only after they were put under stress.
Before resealing an RV, check the sealant requirements for the specific roof or exterior material and follow the manufacturer’s preparation instructions. The tests show how differently these products can behave once they leave the tube.
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