Damp is the number one killer of campervan conversions. Proper waterproofing during the build prevents it.
Sources of Moisture
- Condensation (from breathing, cooking, drying clothes)
- Rain ingress (through roof vents, window seals, seams)
- Ground moisture (soaking up through the floor)
- Gaps in the van body (factory seams, bolt holes)
Floor Tanking
Tanking means applying a waterproof membrane to the plywood floor before installing any covering.
- Paint the plywood with Sika Primer
- Apply Sikafloor or similar tanking membrane (2 coats)
- Seal edges with Sikaflex 221 where the floor meets the van walls
- Let cure for 24 hours before fitting flooring
Body Sealing
- Seal ALL factory holes (unused seatbelt mountings, cable entries)
- Apply Sikaflex 522 to roof seams and gutters
- Replace any corroded sealant around windows and roof lights
- Use butyl tape behind all fittings screwed to the van body
Vapour Barrier
Fit a vapour barrier (breathable membrane) between the insulation and the interior plywood. This prevents warm moist air from reaching the cold metal body and condensing. A Tyvek-style membrane (£20 per 10m roll) is ideal.
Conclusion
A properly tanked floor and sealed van body prevent 90% of damp issues. Do it during the build — fixing damp later is ten times harder.
