Motorhome Damp Repair: From Detection to Full Remediation
A professional approach to diagnosing the source of damp ingress, drying out the structure, repairing damaged panels, and preventing recurrence.
What This Is
Damp is the most common and most damaging problem in motorhomes and caravans. This guide takes you through the complete remediation process from diagnosis to repair.
Tools & Parts Required
- Protimeter damp meter
- Dehumidifier
- Heat gun
- Sikaflex 512 sealant
- Sealant gun
- Panel adhesive
- Replacement ply or foam board
- Jigsaw
- Screwdriver set
Step-by-Step Instructions
- 1
Using a Protimeter damp meter, systematically map all areas of elevated moisture. Record readings on a sketch plan. Readings above 20% WME require investigation; above 30% indicates active damp needing urgent attention.
- 2
Work from the highest damp reading outward to find the entry point. Common locations: cracked sealant around windows, roof lights, and roof-mounted equipment; failed corner moulding seals; cracked GRP panels. Use a hosepipe to test suspect areas — have a second person inside watching for water entry.
- 3
Before any internal repair, the ingress point must be sealed. Remove all old sealant with a sealant remover tool and clean the surface thoroughly. Apply Sikaflex 512 in a continuous bead, tooling it into the joint. Allow to cure for 24 hours before testing.
- 4
Place a dehumidifier in the vehicle and run it continuously. Use a heat gun on low setting to warm affected panels. Allow at least 48–72 hours for mild damp, up to 2 weeks for severe cases. Do not begin repairs until readings are below 15% WME.
- 5
Once dry, probe the affected area with a screwdriver. Sound timber will be firm; rotten timber will be soft and crumbly. Minor softening can be stabilised with a penetrating timber hardener. Severely damaged sections must be cut out and replaced.
- 6
Cut out damaged sections with a jigsaw, cutting back to sound material. Replace with marine-grade plywood (structural sections) or rigid foam board (non-structural panels). Bond in place with panel adhesive and secure with screws where appropriate.
- 7
Refit wall panels, floor coverings, and furniture. Check that all fixings are tight and that no new gaps have been created. Apply a final coat of sealant to any internal joints that may be exposed to moisture.
Common Mistakes to Avoid
- Repairing the interior before fixing the ingress point — the damp will simply return
- Rushing the drying process — inadequately dried timber will continue to rot under new panels
- Using standard silicone sealant instead of Sikaflex — standard silicone does not bond to GRP and will fail
When to Call a Professional
Extensive structural damage, delaminated GRP panels, or damp affecting the floor structure should be assessed by an NCC Approved Workshop.
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