Sealants — a sticky subject

In the Airstream universe you will find a curious phenomenon: passionate debates about sealants. That’s because the constant movement of all parts on the road causes all travel trailers to leak eventually, and a good sealant is our first line of defense against rain penetration.

The aluminum construction of an Airstream is another reason Airstreamers love to debate sealant. Common sealants like silicone don’t adhere as well to aluminum, so we have to use polyurethane sealants that are more expensive but stick like crazy and stay gooey for a long time.

Rather unfairly, Airstreamers get more of this debate than owners of other brands, mostly because Airstreams have been around for so long, and so many of them remain on the roads after decades of use.

The good news is that if you've recently bought a new Airstream, you won't have to worry about this for a long time. Modern Airstreams use high-grade "elastomeric" sealants (meaning they can stretch without breaking their seal as the travel trailer moves down the road) that are incredibly long-lasting, even in tough conditions of harsh sun and frequent rain.

Where do you need to re-seal?

First off, the riveted seams of an Airstream should never need re-sealing, unless the body has been physically damaged (dented). For years Airstream has been using Acryl-R Seam Sealer, and along with the rivets it amounts to a permanent seal.

The edges of roof penetrations such as the plumbing and ceiling vents, TV antenna, skylights, solar panel mounts, etc., are the usual spots that need re-sealing. Even in those spots you only need to think about replacing the sealant when it's:

• pulling away (gapping)
• cracked or missing
• known to be leaking
• or a roof item (fan, etc) is being replaced.

If someone tries to sell you on getting everything on the roof "re-sealed" without clear proof of those indicators, hold onto your wallet.

You also don't need sealant around many other types of penetrations that have their own neoprene gaskets, such as the air conditioner, late-model clearance lights, and small items like the exterior power outlet.

Which sealant should you use?

In the old days the general-purpose sealant of choice was called Vulkem, and you’ll still hear vintage Airstream owners talk about it. Like the modern sealants, it had a marvelous ability to seal gaps tightly, stick to aluminum, and remain slightly tacky beneath the surface for many years.

These days it has been supplanted by a more modern formulation that carries the same name, as well as a few other new products. Most of the recommended modern sealants have certain characteristics in common: they are polyurethane (not silicone) based, sticky like hot salt-water taffy and they adhere to aluminum and plastic like glue. Once cured, they flex a lot without breaking their seal, and they are designed for exterior use (only) so they are UV-resistant and completely waterproof.

As long as you choose a sealant that meets those criteria, you can use any particular one that fits your needs. Popular choices include Sikaflex 221, TremPro 635, Vulkem 116, AdSeal, and others.

Where to shop

Finding appropriate sealant is sometimes difficult. It's easiest to shop online, but if you are in a rush to fix a leak, check hardware stores for a construction sealant that is guaranteed waterproof, UV stable, approved for outdoor use and which adheres to aluminum, painted surfaces, and plastic.

You can always go to the local RV store and find acceptable alternative products, but in my experience white-box RV store products seem to be made for the disposable RV market because they often break down too quickly and start to crack, then leak.

Sticky situations

There are a few challenges with using many sealants. First off, the fumes of some sealants are stinky and toxic, which means you have to take precautions so that the fumes don't collect if you are lucky enough to have an indoor space to work on your Airstream.

Second, polyurethane sealants are trickier to shape and smooth than silicone, because they stick to everything. The old “wet finger” trick that you use with silicone won’t work—these sealants will stick to your wet finger. Wear disposable vinyl gloves and bring along a bunch of paper towels for cleanup.

Third, keep in mind that the good sealants tend to cure very slowly. For example, Vulkem cures at the rate of just 1/16″ of an inch per day at 75 degrees F and 50% humidity. You’ll want to allow a few days for a good cure before exposing the new sealant to weather.

Saving sealant

It’s hard to save the leftovers. Once you’ve opened a tube of sealant, take some care to re-seal it well for storage. There are many techniques to try to seal the tube, such as putting a golf tee in the opening, covering with the tip of a rubber glove, using food saver vacuum bags, hot gluing the tip, and using commercially-available storage caps of various designs.

Don’t freeze it—that method can cross-contaminate other items in the freezer (your ice cream might taste funny after a while) and the manufacturers of the sealants generally don’t recommend storing at that temperature.

Whatever you do, don’t expect opened sealant to still be usable in a year. Even if you take tremendous effort to close up the tube against outside air and moisture, it will probably cure to a solid lump in a few months.

Safety first

The sealants discussed here are fairly safe but you should take a moment to read the fine print on the tubes before using them. Avoid skin contact or breathing of the vapors in a confined space. (That also goes for chemicals used to clean up afterward.) There are recommended temperatures at which you should apply sealants, and recommended techniques for application, cleanup, and storage.

Sealing the Airstream against leaks really isn’t rocket science. Generally the sealants last a long time, so the old days of climbing on the roof to “re-caulk the seams” every year are over. When replacement is eventually needed, making a good choice of product will be a key part of keeping your Airstream dry and happy.