The Roof System

A factory RV roof is a mechanically-terminated single-ply assembly. The sheet is rolled out over the deck, adhered in places, cut open at every penetration, and clamped at the perimeter under a termination bar and the drip rail. Everything holding it in place is at the edges and at a few hundred fastener points.

That design has one useful property — it is cheap to build — and several failure modes. The sheet can release from the deck and bubble. Wind can get under a lifted edge. Every penetration is a cut in the membrane bridged only by sealant. And the sheet itself ages, thins, and hardens.

A sprayed polyurea roof is fully bonded across 100% of the deck. There is no unadhered area for a bubble to form in and no edge for wind to get under. The membrane runs continuously up and over every flange, so there is no cut and no sealant bridge. It is the difference between a sheet laid on a roof and a membrane that is part of the roof.

At 40–60 mil it is also substantially thicker than the 45-mil EPDM or 45-mil TPO it goes over, and unlike those it does not thin with age.

EPDM. The hardest prep and the most common roof. Two full passes with Super Orange Cleaner with a rinse between, because the chalky plasticizer layer is thick on any roof over eight years old. Water-sheet test after: if water beads anywhere, wash that area again. Then 7001 Primer across the field and doubled at every detail.

TPO. One thorough cleaning is usually enough — it does not chalk. But it is slick, and primer is mandatory. Do not talk yourself out of it because the surface looks clean; clean TPO is exactly the problem.

Fiberglass. Scuff any remaining gelcoat gloss to break the surface, then clean twice to remove mold-release wax, then prime. Wax is the single failure mode on fiberglass and it is invisible.

Aluminum. Degrease, scuff the oxide layer, prime. Pay extra attention to rivet lines — dissimilar-metal corrosion under fastener heads is common and those areas need to be cleaned back to sound metal.

Previously coated roofs. Test first: work a putty knife under an edge and pull. If the old coating stays put, clean it, scuff it, and prime over it. If it lifts in sheets, all of it has to come off. Acrylic and silicone RV roof coatings in particular are frequently not overcoatable.

• Strip the sealant first. Every bead around every vent, fan, AC shroud, skylight, antenna base, and solar foot comes off to bare flange. Plastic scraper and a heat gun on low.
• Address the substrate. Small tears in the old membrane over dry, sound decking get cut, bonded down, and coated. Anything over wet decking stops the job — that is a replacement.
• Clean and prime. Field first, then a second primer pass at every flange, seam, and termination.
• Detail coat. Build the 80-mil areas before the field goes on — flanges, cap transitions, and the termination edge.
• Field pass. 40–60 mil across the deck, tying into the detail work.
• Terminations last. Wrap the membrane over the drip rail so water leaving the roof is running on polyurea the whole way, not stopping at an edge.