Preventing Damp in Your Motorhome
Practical steps to prevent damp ingress — the most costly problem affecting motorhomes and caravans.
What This Is
Damp is the single biggest cause of expensive repairs in motorhomes and caravans. Water ingress through failed seals can cause structural damage, rot, and mould that costs thousands to repair. Prevention is far cheaper than cure.
Tools & Parts Required
- Damp meter (recommended)
- Sealant gun with motorhome-grade sealant
- Isopropyl alcohol or panel wipe
- Masking tape
- Putty knife or sealant tool
Step-by-Step Instructions
- 1
Inspect all external seals twice a year — spring and autumn. Focus on roof joints, window frames, door frames, aerial and vent surrounds, and any external fixings.
- 2
Look for cracks, gaps, or lifting in the sealant. Even a hairline crack can allow water to enter over time.
- 3
Use a damp meter to check interior walls, particularly below windows, in corners, and around the floor edges. A reading above 15% moisture content warrants investigation.
- 4
Before resealing, remove all old sealant from the joint using a putty knife. Clean the surface thoroughly with isopropyl alcohol and allow to dry completely.
- 5
Apply masking tape either side of the joint for a neat finish. Apply motorhome-grade sealant (Sikaflex 512 or equivalent) in a continuous bead, pressing firmly into the joint.
- 6
Smooth the sealant with a wet finger or sealant tool. Remove the masking tape before the sealant skins over (within 5–10 minutes).
- 7
Allow the sealant to cure fully before exposing to rain — typically 24 hours. Do not stretch or stress the joint during curing.
- 8
Ensure roof vents and skylights close fully and their seals are intact. Replace vent lid seals if they are compressed or cracked.
Common Mistakes to Avoid
- Using silicone sealant instead of motorhome-grade sealant — silicone does not bond well to GRP and fibreglass.
- Sealing over old sealant without removing it — the new sealant will not bond properly.
- Ignoring the roof — most damp ingress starts at the roof joints.
- Not checking after heavy rain — water finds the smallest gaps.
Safety Warnings
- Use a stable ladder and have someone with you when inspecting the roof.
- Do not walk on the roof unless it is rated to take your weight — most motorhome roofs are not.
When to Call a Professional
If your damp meter shows readings above 20%, or if you find soft or delaminating walls, the structure may already be damaged. A specialist damp repair company should assess the extent before you attempt any repairs.
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