Camper Roof Sealant

Water gets into a travel trailer at the seams: the roof-to-cap joint at the front and back, the flanges of every vent, skylight, and air conditioner, the drip rail along each side, and the hundred screw heads that hold it all down. The sealant on those seams is the only thing between the plywood roof deck and the weather, and it has a service life of a few years in the sun.

Resealing is not hard. Picking the wrong product is, because the failure shows up a year later as a soft spot in the ceiling. Self-leveling lap sealant goes on horizontal roof seams, non-sag on vertical ones, Eternabond tape on seams you want to stop thinking about, Geocel-type sealants on sidewalls and trim, and silicone nowhere. Which is right also depends on what the roof is made of, so that’s where this starts.

You need a ladder you trust, a plastic scraper, mineral spirits or denatured alcohol, rags, a caulk gun, and a dry day above 50 °F with no rain forecast for 24 hours. Plan on 2 to 4 hours for a full inspection and touch-up.

Step 1Identify the roof material

Four roof types cover nearly every travel trailer built since the 1990s, and the sealant that works on one can fail on another.

EPDM rubber. The most common on trailers from the 1990s through the 2010s and still used. A synthetic rubber sheet glued to the roof deck. White or off-white on top, black on the underside, which you can see by lifting an edge at a vent flange or under the drip rail trim. Slightly textured, matte, and it chalks: rub a wet finger on it and you get white residue, and the sidewalls streak white after rain. The chalking is normal; it’s how EPDM sheds UV.

TPO (thermoplastic polyolefin). Common since the 2010s. White or light gray the same color all the way through, slicker and glossier than EPDM, does not chalk, often shows a faint fabric pattern from the scrim layer. Sealants bond to TPO less readily than to EPDM, so manufacturer compatibility matters more here.

Fiberglass. A hard gelcoat panel, glossy, no give when you press, taps solid. Common on higher-end trailers and on the front and rear caps of trailers with membrane roofs. Think of it as a boat hull; it takes the same sealants as the sidewall.

Aluminum. Seamed metal panels, mostly on older trailers. Seams every few feet with a bead of sealant on each. It expands and contracts more than the others, which is what kills rigid sealants on it.

If you can’t tell from the roof, check the owner’s manual or spec sheet. “Rubber roof” in sales material usually means EPDM; “TPO” or a brand name like SuperFlex is TPO.

Step 2Match the product to the job

Self-leveling lap sealant: horizontal roof seams, flanges, and screw heads

Dicor 501LSW-1 (white; gray, tan, and dove white versions exist) is the default for EPDM and TPO roofs and is what most trailer builders use at the factory. It flows out after application into a smooth, slightly domed bead, so it fills the gap between a vent flange and the membrane and seals over screw heads without tooling. That same flow means it only works on surfaces close to level; on a slope it runs.

Where it goes: the perimeter of every roof vent, skylight, AC flange, antenna base, refrigerator vent, plumbing vent, and solar mount; the horizontal portion of the front and rear cap seams; every screw head on the roof; and the seam where the membrane meets the side termination bar, if that seam is flat.

Dicor’s data sheet states compatibility with EPDM and TPO membranes and with aluminum, galvanized steel, fiberglass, wood, and vinyl. It is self-adhering: new 501 bonds to old 501 that is clean and still adhered, which is why you don’t have to strip a flange to reseal it.

Cure times from Dicor’s data sheet: skins in about 5 minutes, waterproof in about 4 hours, 80 percent cured in 48 hours, full cure up to 30 days depending on temperature and humidity. The application range on the data sheet is roughly 50 to 100 °F; below about 50 °F it won’t level and may not bond well. Check the current sheet for your tube’s lot.

Non-sag lap sealant: vertical surfaces and caps

Dicor 551LSW-1 is the same family in a non-sag formula. It holds a bead on a vertical surface and can be tooled. It goes on the vertical faces of front and rear cap seams, the roof edge where the membrane wraps down to the drip rail trim, side termination bars that stand proud, and anywhere a self-leveling bead would run off. Same compatibility, similar cure.

Eternabond RoofSeal: long seams, splits, and seams you want permanent

Eternabond RoofSeal is a tape, typically 4 in or 6 in wide, with a thick MicroSealant adhesive layer under a UV-stable facing. Once bonded it is effectively permanent, which is both the appeal and the warning.

Use it on long splits or punctures in the membrane, the full-length roof-to-cap seam when you want to seal it once, the side-to-roof seam on an aluminum roof, and over a flange you never expect to remove. Don’t put it over an AC unit or fan you might replace; removal means a heat gun, an hour, and some of the membrane.

Prep is the whole job. Clean the surface with Eternabond’s cleaner or denatured alcohol until a white rag stays white. On TPO, on weathered EPDM, and whenever the surface is below about 50 °F, apply EternaPrime spray primer and let it flash per the can. Lay the tape without stretching it, overlapping the seam by at least 1 to 2 in each side, then press it with a steel seam roller across its whole width. Eternabond’s instructions call the roller mandatory; hand pressure leaves voids that become channels. The seal is waterproof immediately and the bond keeps building for days.

Eternabond does not adhere over silicone, over uncured lap sealant, or over flaking old sealant; the old material has to come off first.

Geocel ProFlex RV and Sikaflex 221: sidewalls, trim, fiberglass, aluminum

Geocel ProFlex RV is a tripolymer sealant made for the vertical surfaces of an RV: sidewall seams, window and door frames, baggage door trim, corner moldings, the J-rail that catches the drip rail, and the joint between a fiberglass cap and the sidewall. It bonds to fiberglass, aluminum, painted metal, glass, and wood, stays flexible, can be painted, and per Geocel’s data sheet applies to damp surfaces across a temperature range that extends below freezing; verify on the current sheet.

Sikaflex 221 is a polyurethane adhesive sealant for the same sidewall and trim jobs, with stronger adhesion for bonding trim and a paintable, tooled finish. Per Sika’s data sheet it skins in roughly 40 to 60 minutes at 73 °F and cures about 1/8 in per 24 hours. Sika’s roof product for EPDM and TPO is Sikaflex 715, a silane-terminated polymer formulated for membrane compatibility and UV exposure; Sika does not position 221 for roof membranes.

Butyl tape: under flanges, never on top

Butyl tape (1/8 in thick, 3/4 or 1 in wide) is the gasket that goes between a vent flange or window frame and the roof or wall before the screws go in. It never cures, stays tacky, and squeezes out a little when the fasteners are tightened. Trim the squeeze-out with a plastic blade, then seal over the flange edge and screw heads with lap sealant. If you pull a vent, replace the butyl; don’t reuse the compressed old strip.

Silicone: not on the roof, not on the sidewall

Silicone sheds water, which is why it’s tempting. It also releases from most RV surfaces within a season or two and leaves a residue that nothing else will bond to, including new silicone. Once a seam has had silicone on it, every future sealant job starts with scraping to bare material, and on EPDM you often can’t get it all. Lap sealant and Eternabond both fail over silicone residue.

Step 3Seam and location to product

Location	EPDM or TPO roof	Fiberglass or aluminum roof
Vent, skylight, AC, antenna, solar mount flange edges	Dicor 501LSW self-leveling	Dicor 501LSW or Sikaflex 715
Screw heads on the roof	501LSW	501LSW
Front/rear cap seam, horizontal part	501LSW	501LSW or 715
Front/rear cap seam, vertical face	Dicor 551LSW non-sag	551LSW or Geocel ProFlex RV
Roof edge at drip rail / termination bar	551LSW (501 if flat)	ProFlex RV or Sikaflex 221
Long split, puncture, seam to make permanent	Eternabond RoofSeal (EternaPrime on TPO)	Eternabond RoofSeal
Aluminum panel seams	n/a	Eternabond, or 501LSW on flat seams
Under any flange or frame (gasket)	Butyl tape	Butyl tape
Sidewall seams, window and door frames, baggage doors, corner trim	Geocel ProFlex RV or Sikaflex 221	Same

TPO note: membrane manufacturers publish their own compatibility lists. Dicor states its lap sealants are TPO-compatible; Alpha Systems names approved sealants in its care guide. If the roof is under warranty, use what the membrane maker names, and prime for Eternabond.

Step 4Remove what needs removing, leave what doesn’t

Resealing a flange does not mean stripping it. Lap sealant that is intact, adhered, and merely dirty or chalked gets cleaned and recoated. Sealant that is cracked through, lifted at the edges, or peeling comes off, and only that sealant.

Work with a plastic scraper or a wood shim, never a metal blade on EPDM or TPO. The membrane is about 45 mils thick and a gouge is a new leak. Warm stubborn old lap sealant with a heat gun on low; it peels in strips once it lets go. Wipe residue with mineral spirits or denatured alcohol, sparingly, and let it flash off. Don’t use lacquer thinner, acetone, or petroleum-based cleaners on EPDM; they swell it.

Wash the area with soap and water first, then the solvent wipe, and let it dry. Lap sealant applied over chalk sits on the chalk, not the membrane.

Step 5Apply

Lap sealant. Cut the tube tip for a 1/4 to 3/8 in bead. Lay a continuous bead along the seam or around the flange edge, letting it flow onto both the flange and the membrane by at least 1/4 in. Cap each screw head with a dab that covers the head and the washer edge. Don’t tool self-leveling, and don’t spread it an inch thick over the entire flange. A thick mass cures slowly from the outside in, cracks as it shrinks, hides what’s under it, and holds water in the cracks. That is the “cover everything in Dicor” roof you see at every campground, and it leaks worse than the thin bead it replaced.

Non-sag. Same bead, then tool it with a gloved finger or a plastic tool into the seam so it has contact on both faces.

Eternabond. Clean, prime if required, peel the backing a foot at a time, lay it, roll it. Round the corners of the tape with scissors so they don’t lift.

ProFlex or Sikaflex on sidewalls. Bead into the seam, tool to a slight concave, wipe the excess before it skins. ProFlex skins in roughly 30 minutes and is paintable after a day per its sheet.

Lap sealant needs about 4 hours to be rain-safe; a bead rained on in the first hour washes out of the seam.

Step 6Inspection schedule

Every 3 to 6 months, and after hail, a tree branch strike, or a long highway run in heat. Many trailer manufacturers’ warranty terms put the interval at 90 days, and that’s the number to use the first few years.

Look for hairline cracks in the lap sealant surface (UV aging; recoat), lifted edges where a fingernail slides under (bond failure; remove and redo), sealant pulled away from a screw head, and any membrane bubble near a seam (water under it). On the sidewall, brown or black staining under clear sealant is mildew in a failed bond. Inside, press the ceiling at every corner and vent; soft means a leak that’s been there a while.

Symptom → likely cause

What you see	Most likely	Fix
Hairline surface cracks across old lap sealant	UV aging	Clean, recoat with 501LSW
Sealant lifting at edges, fingernail slides under	Applied over dirt or chalk, or over silicone	Remove loose material, solvent wipe, reapply
Sealant run down a cap in tears	Self-leveling used on a vertical face	Remove, redo with 551LSW
Sealant peeled off cleanly, nothing sticks	Silicone residue	Scrape to bare, solvent wipe repeatedly, Eternabond over primer
Ceiling stain at a front or rear corner	Cap seam, vertical portion	Inspect 551 areas and the cap-to-sidewall joint
Ceiling stain around a vent	Flange sealant or a missing screw cap	Inspect the bead and every screw head
Soft spot in the roof deck	Long-term leak	Stop sealing; the deck needs repair

Parts and tools mentioned

• Dicor 501LSW-1 Self-Leveling Lap Sealant (also 501LSG gray, 501LST tan, 501LSD dove)
• Dicor 551LSW-1 Non-Sag Lap Sealant
• Eternabond RoofSeal tape, 4 in; EternaPrime primer; steel seam roller
• Geocel ProFlex RV (clear or white)
• Sikaflex 221 (sidewalls) and Sikaflex 715 (roof membranes)
• Butyl tape, 1/8 in x 3/4 in or 1 in
• Plastic scraper, heat gun, mineral spirits or denatured alcohol, lint-free rags
• Caulk gun, utility knife, scissors, ladder with a stabilizer

Questions people ask next

Can I put new Dicor over old Dicor? Yes, if the old sealant is clean, dry, and still bonded. Dicor states its lap sealant is self-adhering. Remove only the sections that are cracked through or lifting, then recoat.

Is Eternabond really permanent? Functionally, yes. Removing it takes heat and patience and on EPDM it usually takes some membrane with it. That’s why it goes on seams you don’t plan to open and not over an AC unit or fan you may replace.

My roof is TPO. Does Dicor work on it? Dicor states its lap sealants are compatible with TPO. Clean the surface thoroughly; TPO’s slicker surface is less forgiving of residue. If the roof is under warranty, use whatever the membrane manufacturer lists.

What about roof coatings? Liquid roof coatings are a different product: applied over the entire membrane to restore it, and some are not compatible with TPO. They don’t replace seam sealant. Seal the seams first, then decide whether the whole roof needs coating.