RV Engineer answers: “Is silicone sealant the worst thing ever for your RV?”

By Andrew Herrick
If you like poking bears, stirring up hornets, and awakening sleeping dogs, then you’ll love the question, “Should I use silicone sealant on my RV?”

Many RV owners would rather swallow a live June bug than spread silicone caulk over their rigs. “Silicone is the worst possible product you could use,” they warn. “It will peel, and nothing will ever stick to it again!”

Should you believe these fireside horror stories of silicone gone awry? If silicone is so bad, why are some RVs sealed with silicone straight from the factory? And what should you be using instead?

Let’s back up—put the silicone back in the tube, as it were. Why all this hullabaloo about silicone in the first place?

Silicone protects your RV—and your warranty!

If you’re a new RV owner and you’ve neglected your Owner’s Manual, you might be surprised to learn that most manufacturers insist you inspect your exterior seals every 90 or 180 days and re-seal every year. This includes every window, door, fan, hatch, seam, and screw. Almost everything on the outside of your RV partially depends on a self-leveling or skim sealant, like silicone, to stay dry.

And should you be unfortunate enough to have a leak within your warranty period, the first thing the Warranty Department will check is proof that you’ve meticulously maintained your exterior. Because (fun fact) RV limited warranties generally do not cover “damage or loss related to water leaks from failure to properly maintain the RV, such as failure to properly maintain exterior seals.” That’s from the 2023 Forest River Limited Towable Warranty.

So this silicone stuff is serious business. Not only is it the first line of defense against Mother Nature, but if you don’t catch a sealant failure, you’re probably on the hook for any damages.

So grab a caulk gun (this one is the best), snap on some nitrile gloves, and let’s inspect your RV.

How to remove silicone caulk without breaking the Third Commandment

Here’s why everyone will tell you not to use silicone: “Nothing sticks to it!” and “You can’t get it off!” If those warnings sound oxymoronic … well, let me explain.

Strictly speaking, the caution that nothing sticks to silicone isn’t true. New silicone will bond with old silicone—but there’s some fine print. It only works …

• If the surfaces are completely cleaned of dirt, mold, and other contaminants; and
• If the new silicone has the same crosslinking chemistry as the old (acetate, oxime, alkoxy, amine).

Unfortunately for you, manufacturers are more likely to use an oxime (neutral cure) silicone, and if you’re shopping at a Big Box store, you are more likely to have acetoxy silicone, which smells like vinegar. The two won’t bond. And good luck scrubbing a year’s worth of dirt and grime off any cap sealant!

To add insult to injury, very few other sealants—urethane, co-polymer rubber, latex acrylic—play nicely with silicone. Silicone has infamously low surface energy. It’s the social wallflower of chemicals.

So what’s an RV owner to do?

Attempt 1: Scrape it off

If you can’t (realistically) get new sealant to stick to old sealant, you will resolve to scrape off the old stuff using a knife, oscillating tool, or putty scraper. And that’s where the curse words really get colorful, because silicone sealants leave a tenacious, oily residue, their perfidious Parthian shot. If you lay a fresh bead of sealant on that residue, you’ll be able to peel it off with your fingers afterward.

Attempt 2: Melt it off

So RV owners turn to ol’ trusty: a chemical in a can. But you will quickly discover that most consumer solvents don’t really dissolve silicone so much as they soften it into a gummy, sticky mess. Typical consumer solvents like denatured alcohol, acetone, and mineral spirits will require multiple applications (plus elbow grease) to fully remove the residue. And because most industrial solvents that would readily remove silicone will also damage your membrane roofing, you’re facing a Catch-22.

Attempt 3: Grind it off

Next, in desperation, out comes the scouring pad or the wire brush. And that’s how this saga ends for most RV owners: grinding, sanding, scouring away on their hands and knees, nostrils burning with chemical fumes from failed attempts, damning silicone (and the RV manufacturer who used it) to Dante’s Ninth Circle of Hell.

So why do some manufacturers use the stuff in the first place?

Why do RV manufacturers use silicone sealant?

Here are several reasons RV manufacturers have used silicones for exterior sealants:

• Silicones are easy to apply. They gun fast and tool easily.
• Silicones are reasonably non-toxic. Many other sealants contain harmful solvents requiring high rates of ventilation and zero skin contact.
• Silicones are affordable. Some larger RV manufacturers would spend millions of dollars a year by switching to urethanes.
• Silicones are available in a higher grade. Most manufacturers have access to much, much higher quality silicone sealants than you do.

However, I’m seeing a trend away from silicone sealants. Manufacturers are moving to synthetic rubbers and single-part urethanes like OSI Quad, Geocel 2300 MHRV, and Sika 211.

A cautionary tale: Where you buy your silicone matters

One time, I was chatting on the phone with an Applications Specialist from a major chemical company, and he let me in on a little secret: It’s a highly consolidated industry. There are only a handful of silicone elastomer manufacturers across the globe, such as Dow, Elkem, and Shin-Etsu Chemical. And guess what? Low-cost silicone sealants are filled with the lowest grade of silicone polymer. The good stuff goes into electrical insulation, medical equipment, and aerospace parts.

Then the plot thickens! These OEMs sell their polymers to formulating companies. And the potion-master chemists at these companies will brew new concoctions of caulks, sealants and adhesives. Some of these companies sell products under their own name, but many of the off-brand caulks you see (looking at you, Amazon) are just repackaged private-label brands from a formulator who offers contract packaging services. Same product, different sticker.

So, if you do purchase silicone caulk for your RV, go to a reputable building supplies store and buy the expensive stuff. Don’t settle for the cheap stuff where the tube probably cost more than the sealant! And finally, stay away from anything “siliconized,” which will not survive the harshness of the outdoors!

Should you use silicone caulk on an RV?

My two cents: I think you’re better off picking a different battle. A good silicone can work for your RV, but there are easier options.

Personally, I use Geocel Proflex RV (or Geocel 2300) for most non-sag applications. My other personal favorite is Sashco Lexel. It’s not a great choice for manufacturing because of the high percentage of solvents, but with soapy water, it tools like a dream. Makes me look much more skilled with a caulk gun than I actually am.

Which sealant do you like to use? Have you ever gotten on the wrong side of silicone removal? Tell me your stories in the comments!

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