RV Structure, Body, Roofing, and Sealants
Structure questions concentrate on water: where it enters, how it travels, and how to stop it permanently. You are also expected to know roof membrane types, the sealants approved for each, and how laminated sidewalls and floors are built.
Membranes and sealants
- EPDM is the black rubber membrane, TPO is white and can be heat welded, and fibreglass and aluminium roofs have their own rules. Each has approved cleaners; petroleum distillates void EPDM warranties.
- Lap sealant comes in self-levelling for horizontal surfaces and non-sag for verticals. Sealant brands are not freely interchangeable across every membrane.
- Butyl tape goes under flanges; lap sealant goes over fasteners and edges. That is a two-step joint, not one.
- Sealant has a service life measured in months, not years. Inspect every 90 days and reseal cracks before they open into the deck.
Structure
- Vacuum-bonded lamination stacks a filon or fibreglass skin, luan, foam, and aluminium or wood framing. Delamination shows as soft spots and wavy skin, confirmed with a moisture meter against a dry baseline.
- Water runs downhill and along the deck. Find the entry point above and uphill of the stain.
- Common entry points: roof penetrations, clearance lights, window frames, slide seals, beltline moulding, and corner caps.
Worked example
A ceiling stain sits near the rear vent, but the roof directly above is dry. Trace uphill along the deck and find cracked sealant on the uphill side of the vent flange; water runs along the luan and shows at the stain. The repair is to remove the old sealant, clean with an approved cleaner, prime if the membrane requires it, bed the flange on butyl tape, then cover fasteners and edges with self-levelling lap sealant. Recheck with a moisture meter after rain. If the luan is soft, the deck is cut out and replaced, which changes the estimate.
Traps
- Applying silicone to EPDM or TPO, where it will not hold long term.
- Sealing over a wet substrate and trapping moisture inside the deck.
- Pressure washing a membrane or walking a non-walkable roof.
- Assuming the stain marks the leak location.
- Forgetting clearance lights and the beltline, which leak more often than roof vents.