Nerd Battle of the Best RV Self-Leveling Roof Sealants

Are you a fellow sufferer of analysis paralysis? I am. Choosing a self-leveling sealant is enough to set me back three Ibuprofen pills. Options abound. And as an RV repair technician, I must carry sufficient stock to re-seal all roof types, all colors, at any time. I don’t want to stock $700 worth of self-leveling sealants, so how can I consolidate my choices while providing top quality?

Admittedly, like some other articles of mine, this one is needlessly nuanced. If you’re simply after the best self-leveling caulk, then here’s what I’d tell you:

Choose a self-leveling caulk that is compatible with your roof material type.
Thoroughly remove or clean any existing caulk to ensure the best adhesion.
Inspect your RV roof sealants twice a year: spring and fall. Look for bubbling, cracking, peeling, or disintegration.
You get what you pay for. (It’s cheaper for a reason.)

If you follow those four rules, then you’re already ahead of the curve. Any RV-approved self-leveling sealant, properly applied, will do the job. Either use a “universal” self-leveling sealant like Dicor 501, Alpha Systems 1021, or XTRM-Ply Universal, or even better, use the recommended sealant by your RV manufacturer.

Now, if you’re curious (like I am) about the science behind these caulks and sealants, then let’s put on our nitrile gloves and safety glasses, and dive in. And I’ll tell you a few of my favorite choices (and not-so favorites).

Wait – Is It Called “Self-Leveling” or “Lap” Sealant?

In the RV space, we can get a little lazy in our vocabulary. For instance, we use the terms “caulk” and “sealant” interchangeably, even though caulk normally refers to a more rigid glazing or joint-filling compound.

We may refer to self-leveling sealant as “roof sealant,” since the roof is the only place it is used on an RV. Or we might call it a “horizontal” sealant, as opposed to the stiffer, non-sag “vertical” sealants used on the sidewalls.

Self-leveling sealants are also called “lap sealants,” partially to distinguish them from the self-leveling joint fillers of the concrete industry. (In case you’re wondering, no, I wouldn’t recommend a construction expansion joint sealant like MasterSeal SL 1. I tested it once, and it was too thin for RV use. It poured rather than slumped, and it didn’t cover all the screw heads.)

The preferred term, I believe, is “self-leveling lap sealant,” which I often shorten to “self-leveling sealant.” But feel free to mix n’ match terms to your liking!

Introduction to RV Self-Leveling Roof Sealants

I’d be embarrassed to tell you how much time I’ve spent over the years researching self-leveling sealants: first as a design engineer, now as a repair technician. Information is not always forthcoming. Some OEMs don’t even publish SDS or tech data sheets unless requested – but everyone says they’re the best, of course.

What does it mean to be “the best”? Well, as you can imagine, everyone measures by a different measuring stick. Some tout their products because they are the easiest to apply and the fastest to skin over (cough, Dicor, cough). Some promise universal adhesion compatibility, some advertise longest life, some lowest cost. Which RV roof self-leveling lap sealant is really the best?

Like all good engineers, I can only give one answer: It depends. Choosing a caulk is always an optimization problem. You’re choosing trade-offs. There are so many types of construction adhesives! Are they plastomeric or elastomeric? Clear or colored? Moisture-cure, solvent-cure, or non-reactive? What’s the chemical base: Silicone, acrylic, butyl rubber, urethane, polysulfide, silane-modified polymer, MS hybrid polymer? What’s the skin time vs. the cure time? What’s the minimum and maximum application temperatures of sealant and surface? Can the uncured sealant be tooled with alcohol or soap? Is it cleanable with water, mineral spirits, acetone, or some other solvent? Is ventilation or a mask required during application? What’s the modulus, the shrink rate, the service elongation, the UV resistance, the water resistance, the slump resistance? Is it paintable?

It’s enough to drive you bonkers. That’s why we trust OEMs who hire chemical engineers to create these witches’ brews and sell it to us in 10-oz tubes!

P.S. Durability is not equivalent to adhesion. Stickier is not always better. Yes, self-leveling sealant should stick to the roof, but not permanently! It may need to be removed, after all, such as when replacing a skylight or a ceiling vent. If the sealant exhibits tenacious adhesion, then you’ll destroy the roof trying to scrape it off. You want the Goldilocks solution: something in the middle.

The Big Three: The “Universal” RV Lap Sealants

To my knowledge, there are three popular “universal” RV self-leveling sealants. These are formulated for easy application on and compatibility with the common RV roof materials: EPDM, TPO, PVC, fiberglass, and painted aluminum.

Generally, these universal sealants are compatible with all common RV roofing substrates. However, some may require a primer or adhesion promoter on specialty substrates like low-surface-energy plastics like polypropylene (PP) or polyvinyl chloride (PVC). Some will stain bare metals.

Dicor 501 Lap Sealant*
Alpha Systems 1021 Self-Leveling Sealant
XTRM-Ply Universal Self-Leveling Sealant

*Dicor also sells 502, a tweaked formulation designed for ease of application for RV manufacturers. But it’s NOT compatible with PVC roofing membranes.

Personally, I don’t use Dicor 501 (or 502) because I’ve witnessed too much cracking from excessive shrinkage. Dicor 501 has a solids content of 67.5%. That means 32.5% of what comes out of the tube is going to vaporize and disappear into the atmosphere. Too much solvent can cause shrinking, cracking, and pinholes.

Alpha Systems 1021, its direct competitor, has a solids content of 77%, which means it should shrink and crack less (all else being equal). XTRM-Ply Univeral has a similar solids content of 78%. (I obtained technical data sheets from LaSalle Bristol to confirm this).

Other self-leveling sealants, like Alpha Systems 5121 or SikaFlex 715, are 100% solids because they are moistured-curing, not solvent-curing.

Speaking of solvent-curing sealants … most of the solvent-curing sealants tend to skin over quickly but take several days (or even weeks) to fully cure. Even when cured, they don’t harden; they stay pliable, like bubble gum or butyl putty. In contrast, moisture-curing sealants are more solid and rubbery when cured. (A third type, 2-component reactive sealants, is not used amongst RV roof sealants).

I’ve used lots of Alpha Systems 1021 and XTRM-Ply Universal as general-purpose lap sealants. I like them both, but I find the viscosity varies by color. Beige XTRM-Ply Universal self-leveling sealant, for instance, seems less fluidic compared to the white or gray.

With that said, too much fluidity isn’t always a good thing. I’d rather my self-leveling be a little on the thick side, even if it stays a little lumpy. If it’s too flowable, it may not maintain the thickness to cover screw heads and other protrusions. Some RV roof sealants are specifically marketed as semi-self-leveling, meaning they slump but stay where you put them!

Why Does No One Know About These Self-Leveling Roof Sealants?

SikaFlex 715
Heng’s NuFlex 311

SikaFlex 715 is one of those semi-self-leveling sealants I was talking about. It’s a cross-linking one-component silane-terminated polymer sealant (say that five times fast!)

Notice the word “cross-linking”? That means the cured compound is far more elastic and solid than the typical RV flowable sealant, which is more gum or putty-like. 715 is more resistant to abrasion and less likely to shrink and crack. SikaFlex was specially formulated for EPDM; the OEM has issued no recommendations for PVC or olefin (TPO) membranes. I’ve heard it’s popular for Airstreams, as well.

For some reason NuFlex 311 seems to be the redheaded stepchild of the family of RV self-leveling sealants. It’s a flowable, one-part, neutral-cure, elastomeric silicone sealant. Besides it’s neutral-cure, it releases non-corrosive, non-yellowing alcohols while curing. Cheaper acetoxy-cure silicones release acetic acid while curing, which is corrosive and staining to bare metal and masonry.

Anyway, NuFlex 311 has been recommended by Winnebago for their fiberglass motorhome roofs, and it’s pretty good stuff! I think a lot of RVers are scared away by the word “silicone,” even though there’s a world of difference between the good silicone and the bad. Silicones should be mechanically removed before resealing, however, which normally requires plastic chisels and rubber abrasives.

What About Specialty RV Self-Leveling Lap Sealants?

There are plenty of specialty RV roofing sealants designed for particular membranes or particular uses. Generally, these high-performance RV roof sealants have more adhesion and less shrinkage than the solvent-based universals. Some of them include:

Dicor Ultra Self-Leveling Sealant
XTRM 100 Self-Leveling Sealant
Alpha Systems 5121 Self-Leveling Sealant

Dicor is well aware of the lackluster reputation of its 501/502 products, I would guess. In recent yeras, they’ve launched Dicor Ultra, a high-performance polyether sealant that contains no solvents or isocyanates and is non-yellowing. Use on polypropylene, TPO, and EPDM requires a primer. I haven’t used this stuff myself.

XTRM 100 is specially formulated for the XTRM-Ply PVC roofing system. As a low-surface-energy, PVC won’t bond to many all-purpose selanats. XTRM 100 is equivalent to Manus-Bond 76AM, which is an excellent all-around adhesive sealant.

Alpha Systems 5121 is formulated for the brand’s older AlphaPly EPDM membranes, which will permanently swell if 1021 lap sealant is applied instead. I do like the sealant, though, since it’s 100% solids, so I’ve also used it on Class B metal roofs. It’s semi-self-leveling, so it doesn’t puddle in a smooth bead like Dicor 501 does. You’ll need to finesse your caulk gun technique!

But What About “Brand X” for the Best RV Self-Leveling Roof Sealant?

There are many RV lap sealants I haven’t mentioned. If you go with an RV roof coating, the OEM will want you to use their self-leveling formulation. Tremco will recommend their TremPRO RV Roof Sealant; Henry’s will recommend their 884 Tropi-Cool Roof Sealant; Liquid Rubber will recommend their RV Lap Sealant. I have not yet used most of these products and cannot speak to their quality, although I’m intrigued by the TremPRO product and would like to give it at try.

As I mentioned earlier, there is an entire “other” class of self-leveling sealants like Masterseal SL1 1, DAP AMP, Tremco Vulkem 45SSL, etc. These are expansion joint sealants formulated for the concrete and masonry industry, and in my experience (albeit limited), they are normally too runny for use on RV roofs.

There are other private-label brands as well. I speculate (although I haven’t verified) than house brands like RecPro or Camco are probably repackaged from one of these other manufacturers. I haven’t used any of the Amazon knock-off brands like ToughGrade, Survol, or Ziollo. Unless they explicitly say otherwise, I usually assume Amazon-only brands are just repackaged from somebody else.

But … What About Flex Seal??

For God’s sake, people, stop using Flex Seal on an RV roof! This stuff does not last! I’ve scraped quite a bit off customers’ roofs. If it worked, they wouldn’t be calling me, would they?

Ask The RV Engineer