I’ve been saying the same thing to customers for over twenty years: water is the most expensive thing that can happen to your RV. Not in the sense that water is costly to buy, but in the sense that water intrusion through a failed roof seal is the single most common cause of the catastrophic, expensive damage that writes off rigs that otherwise have years of service life in them. Delaminated walls, rotted floor decking, destroyed cabinetry, compromised structural framing—all of it starts with a small gap in a sealant bead that would have taken five minutes and fifteen dollars to fix.
Lap sealant is the specific product that seals the seams, edges, and penetrations on your RV’s roof—the lines where the roofing material meets the vents, air conditioners, antennas, and edges of the roof surface. It’s a flexible, self-adhering compound that bridges these transitions and creates a watertight seal that moves with the RV as it flexes, rather than cracking like a rigid caulk would. It’s the last line of defense between your interior and everything the sky can throw at it.
This roundup covers the best lap sealants we carry at the RV Upgrade Store—from the industry-standard Dicor self-leveling formula to capable alternatives that offer different performance profiles for different applications and roof types.
Best for: Vertical and angled roof surfaces where a self-leveling sealant would run before curing, and for all-around roof penetrations, vents, and edge transitions on EPDM and TPO rubber roofs
Dicor has been the reference standard for RV roof lap sealant for so long that “Dicoring the roof” has become a verb in the RV community—like “Googling” something, it’s become shorthand for the entire category of roof sealing. That kind of brand recognition doesn’t happen by accident; it’s the result of a product that genuinely works, formulated specifically for the rubber roofing materials—primarily EPDM and TPO—that dominate the RV market.
The 551LSW is Dicor’s non-sag formula, which means it maintains its position after application rather than flowing under gravity as the self-leveling formula does. This makes it the right choice for vertical surfaces—the sides of vent bases, the edges of air conditioner flanges, and anywhere the sealant needs to stay exactly where you put it while it cures. The non-sag formula is also what you want for joints that aren’t perfectly horizontal, where a self-leveling product would run away from the area you’re trying to seal.
Dicor’s chemistry is specifically compatible with EPDM rubber roofing—it bonds to the rubber membrane without causing the chemical degradation that some sealants can produce when applied to EPDM. This compatibility is non-negotiable: using a sealant that isn’t rubber-roof compatible can actually accelerate the failure it’s meant to prevent by attacking the roof membrane around the sealed joint. Dicor’s compatibility with the materials it’s used on is one of the core reasons it became the industry standard.
The cured sealant remains flexible across the temperature range that RV roofs experience—from well below freezing to over 150 degrees Fahrenheit on a dark roof in direct summer sun. That flexibility is essential because an RV roof moves constantly: it flexes under foot traffic during maintenance, it expands and contracts with temperature cycling, and it deflects under the aerodynamic loads of highway travel. A sealant that cracks under this movement is worse than no sealant, because it creates a false sense of security while actually channeling water into the gap it cracked open.
Pro Tip: Apply Dicor lap sealant in temperatures above 40°F for proper adhesion and curing. Cold sealant doesn’t bond properly and can remain tacky or fail to cure completely, leaving a seal that looks correct but isn’t providing effective protection. If you’re doing spring maintenance in a cold climate, wait for a warm day or work in a heated shop to ensure proper curing conditions.
Buy Dicor 551LSW Non-Sag Lap Sealant
Best for: Horizontal roof surfaces where a self-leveling formula provides more complete coverage, for RV owners who want reduced VOC emissions during application, or as a Dicor alternative with strong compatibility credentials
Alpha Systems has built a solid reputation as an RV sealant manufacturer with products that meet or exceed OEM specifications—they supply sealants to RV manufacturers as well as the aftermarket, which means their formulations are vetted against the same performance standards that factory installations require. The 1021 Low VOC is their self-leveling lap sealant, formulated to flow and self-level on horizontal surfaces while providing the rubber roof compatibility that the RV application demands.
The low VOC formulation is meaningful for RV owners who are working in confined spaces or who are sensitive to the fumes that traditional sealant formulas produce during application and curing. VOC—volatile organic compounds—are the source of the strong solvent smell from many sealants, and reducing them makes the application experience significantly more comfortable, particularly when working in the enclosed area above an awning or in a storage bay where ventilation is limited.
The self-leveling behavior is the key performance characteristic for horizontal applications. Apply the sealant to the horizontal joint or seam, and it flows under gravity to fill gaps and low spots more completely than a non-sag formula that sits exactly where you put it. Around the base of a roof vent—a horizontal joint where the vent flange meets the roof membrane—the self-leveling formula provides more thorough coverage with less effort than carefully tooling a non-sag sealant into every point of the joint.
Alpha Systems’ EPDM compatibility matches Dicor’s, making this a genuine alternative rather than a compromise. For RV owners who want to try an alternative to Dicor—whether from a desire to shop around, a preference for lower VOC products, or simply availability at a given time—the Alpha Systems 1021 delivers comparable performance on the surfaces where it’s correctly applied.
Pro Tip: Self-leveling sealant has a narrow application window before it begins to skin over, particularly in warm weather. Apply the sealant and leave it alone—don’t try to tool or smooth it after it’s been applied. The self-leveling action does the smoothing for you, and interfering with it after the initial application breaks the surface skin that’s already beginning to form.
Buy Alpha Systems Low VOC Self-Leveling Lap Sealant
Best for: RV owners who need a sealant that works on multiple roof surface types, including EPDM, TPO, aluminum, and fiberglass, or who want a premium polyurethane-based formula with exceptional adhesion and flexibility
Sikaflex is a Swiss-engineered sealant brand with a global reputation in construction, marine, and automotive applications—environments where sealant performance is non-negotiable, and failures are expensive. The 715 is their RV-specific formula, bringing that engineering heritage to the roof sealing application in a polyurethane-based compound that delivers performance characteristics that standard EPDM-specific sealants don’t match.
The polyurethane chemistry is what differentiates Sikaflex from Dicor and Alpha Systems. Where those products are formulated specifically for EPDM and TPO rubber roofs, Sikaflex 715 bonds effectively to a wider range of substrates—rubber, aluminum, fiberglass, and various plastics—making it the right choice for mixed-material joints where two different surface types meet at a sealed junction. The aluminum trim edge where it meets a rubber roof membrane is a classic example: a rubber-specific sealant may not bond as effectively to the aluminum as it does to the rubber.
The semi self-leveling characteristic is a useful middle ground between full self-leveling (which can run on anything other than a perfectly horizontal surface) and non-sag (which requires careful tooling to fill joints completely). The 715 flows enough to self-complete minor gaps and surface variations, but has enough body to maintain its position on surfaces with slight slopes or orientation variations.
Sikaflex’s cured flexibility is exceptional—the polyurethane compound elongates under movement rather than cracking, which is exactly the property you want in a sealant that’s going to live on a flexing RV roof for years. The adhesion strength is also higher than that of typical EPDM sealants, which means the seal holds against the mechanical forces that try to peel it away from the substrate at the edges.
Pro Tip: Sikaflex 715 requires clean, dry surfaces for optimal adhesion—more so than some other sealants. Use Sika’s primer or their surface cleaner on non-porous substrates like aluminum and rigid plastics before applying the sealant. Skipping the primer on these surfaces reduces adhesion strength by a meaningful margin and shortens the effective seal life.
Buy Sikaflex 715 RV Roof Sealant
Best for: A universal non-sag formula compatible with a wide range of roof materials, ideal for vertical applications, and for RV owners who want one sealant that works across different surface types on their rig
LaSalle Bristol has been manufacturing RV-specific products for decades, and the Xtrm-Ply non-sag sealant reflects their understanding of what the RV application requires: a formula that bonds to multiple roof and surface materials, remains flexible after curing, and maintains its position during application and curing without running or sagging.
The “universal” designation refers to the Xtrm-Ply’s compatibility across rubber, fiberglass, aluminum, and TPO roof materials. For RV owners whose rigs have mixed roofing—or for those who maintain multiple rigs with different roof types—a single universal sealant eliminates the need to keep separate products for different surfaces. One tube in the maintenance kit covers every sealing need.
The non-sag formula is appropriate for the vertical and angled applications where gravity would pull a self-leveling sealant out of position—vent base sides, air conditioner flange edges, antenna mounts, and any seal that’s applied at an angle from horizontal. It stays where you apply it, which is exactly what you need when you’re sealing a joint that isn’t lying flat.
LaSalle Bristol’s quality control as an established RV supplier ensures consistent product performance between batches—something that isn’t guaranteed with every aftermarket brand. A sealant that performs consistently is one you can rely on when you’re doing maintenance at a campground far from any supply source.
Pro Tip: When applying any non-sag lap sealant to a roof penetration, start the bead at the highest point of the fitting and work toward the lower points—the direction that water flows on the roof. This application direction ensures that the sealant bead overlaps correctly and that there are no “uphill” gaps where water could be channeled behind the seal.
Buy LaSalle Bristol Xtrm-Ply Non-Sag Roof Sealant
Roof lap sealant is the least glamorous product in RV maintenance, and it’s also one of the most important. The five minutes it takes to inspect and touch up the sealant beads around your roof penetrations every season is the investment that prevents thousands of dollars in water damage. It’s the maintenance item that delivers the highest return of any routine RV care task.
Every product in this roundup is formulated for RV roof applications—the right flexibility, the right adhesion, and the right compatibility with the materials they’re applied to. Don’t substitute automotive or construction caulks, which aren’t designed for the specific movement, temperature range, and material compatibility requirements of an RV roof. Use products built for the application, apply them on schedule, and your roof will keep the inside of your rig dry for years.
If you’re not sure which sealant is compatible with your specific roof material, give us a call at the store. We’ll help you identify your roof type and match the right product to the application.
I’m Bill Rowell, the founder of RVupgrades.com. In 2002, I launched the business to help fellow RV enthusiasts find unique and hard-to-find products. Over the years, it’s grown to offer more than 15,000 items, with a warehouse in Eastlake, Ohio. Having owned and repaired nearly every type of RV, I bring over two decades of hands-on experience to the table. For me, this isn’t just a business – it’s a passion and a way of life that I love sharing with the RV community.
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