How to Reseal RV Roof Seams: Dicor vs Eternabond

Almost every roof leak I ever get called out to traces back to a seam. Not a hole, not a tear — a seam. The factory caulk dried out and cracked, the edge of the cap joint lifted, water found one weak inch and went to work. And every time, the owner asks me the same question: Dicor or Eternabond?

Both are the right answer — in the right place. Both are also the wrong answer in the wrong place. I've sealed roofs both ways for years, and here is how I decide.

Dicor self-leveling: where it wins

Dicor self-leveling lap sealant is the industry standard for one reason: on a horizontal surface it flows out into a smooth, even cap with almost no tooling. Around vents, skylights, air conditioners, vent pipes, antenna bases, screw heads — anywhere the shape is round, curvy, or just awkward — this is the tube I reach for. It sticks to EPDM rubber, TPO, fiberglass, and aluminum, and it stays flexible enough to move with the roof as the rig twists going down the road.

But here is what nobody tells you at the parts counter: it doesn't last forever. UV and heat dry it out over time. Eventually it cracks, and a cracked bead is a leak waiting for the next rain. That's not a failure of the product — it's just how sealant ages. Plan on inspecting it and touching it up, or plan on owning a water-damage repair. Those are your two options.

Eternabond: where it wins

Eternabond tape is a different animal. It's a peel-and-stick sealing tape with an absurdly strong bond, and once it's down, it doesn't crack, doesn't dry out, and basically doesn't come off. For long, straight, flat runs — front and rear cap joints, membrane seams down the roof, slide roof edges — it's about as close to a permanent repair as this industry gets.

So why isn't it on everything? Two reasons. First, tape doesn't do curves. Wrapping it around a round vent or a ladder bracket is asking for wrinkles, and wrinkles are channels for water. Second, the prep is unforgiving. Eternabond will not stick to silicone — period. Not a little bit. If a previous owner globbed silicone on that roof, every trace of it has to come off or the tape goes down over a surface it can't bond to, and you won't know it failed until it leaks.

Prep is the whole job

Whichever product you use, the surface has to be clean, dry, and sound. Scrape off the loose and cracked sealant, scrub the area down, and wipe it with mineral spirits or denatured alcohol so there's no wax, oil, or grime left. Then let it dry completely. If the tape or sealant bonds to grime instead of the roof, you didn't seal anything — you just added a time delay.

Going over old Dicor with tape is fine, as long as you clean it well and knock down any high mounds with a razor so the tape lays flat. Tape over a bumpy bed of old sealant is tape with air gaps under it, and air gaps are future leaks.

And do the work on a warm day. Tape wants warmth to bond properly. Cold application is how you end up with edges that lift the first time the rig gets up to highway speed.

How I lay the tape

Cut your length with a few inches of overlap past the seam, and know exactly where it's landing before the backing comes off — once that adhesive touches down, it's not coming back up. Peel the backing as you go, lay the tape down without stretching it — stretching thins the adhesive and it wants to shrink back — then roll it down hard. A steel roller with real pressure, working from the center out, especially along the outer edges. That pressure is what activates the bond.

One belt-and-suspenders move I use on roof edges that see a lot of wind: a thin bead of Dicor along the leading edge of the tape. It's cheap insurance against edge lift.

Mistakes I see on every other roof

• Using self-leveling Dicor on a vertical or sloped surface — it's called self-leveling because it runs. Dicor makes a non-sag version for vertical edges; grab the right tube.
• Trying to tape round penetrations. Tape is for straight runs. Goo is for shapes.
• Sealing over dirt and chalk. Sealant stuck to grime isn't a seal.
• Any silicone anywhere near Eternabond. Nothing bonds to silicone residue, and silicone over the tape doesn't help either.
• Not inspecting. Whichever product you use, get eyes on those seams regularly. A ten-minute look catches a five-minute fix before it becomes a ceiling rebuild.

Pick the right product for the shape you're sealing, prep like the whole interior depends on it — because it does — and you'll get a roof that keeps its water on the outside, where it belongs.

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