A damp, soft motorhome floor: what to do and how to get through the winter

A floor that gives underfoot by the entrance door is familiar to many owners of caravans more than fifteen years old. There are two causes, and each has a different repair. Mixing them up means wasting money.

One thing to understand from the start: a floor covering does not cure a floor. It only covers it. The cause and the base come first, the finish afterwards.

How the floor is built

In most caravans and motorhomes the floor is a sandwich: a top sheet of plywood, foam insulation and a bottom sheet of plywood. The layers are bonded together and work as one rigid panel.

A campervan is built differently: the metal floor of the body with insulation and plywood on top (see the article on floor build-up). It has problems of its own: condensation on the metal, and rust.

Two different problems

Delamination

In time the adhesive between the plywood and the insulation lets go. The top sheet is no longer supported by the foam and starts to flex.

Signs:

• the floor springs but returns to place;
• there is a crunch or a creak when you step on it;
• no smell, the plywood is dry and pale;
• usually in the walkways: by the entrance, by the kitchen.

There is no water here. It is fatigue of the glue line after years of footfall.

Rot from a leak

Water gets into the floor through a window, a roof light, a body seam, a wheel arch or from the plumbing. The plywood gets wet and loses its strength.

Signs:

• the floor gives and does not spring back;
• dark stains, a smell of damp or mould;
• the plywood crumbles or separates when pressed with a screwdriver;
• usually in corners, under windows, by the washroom, along the sides.

How to check

1. Heel. Walk the whole floor pressing with your heel. Mark the soft areas with masking tape.
2. Moisture meter. A simple pin-type meter for timber is inexpensive. Compare readings on the soft area and on one you know to be dry. A clear difference means water.
3. From below. Look under the caravan: dark stains, underbody protection coming away, run marks.
4. The source. Check the window and roof-light seals, body seams, arches and water connections.

If there is moisture, the leak is found and fixed first. While water is still getting in, any repair is temporary.

Repairing delamination

The standard method is injection. A grid of holes is drilled in the top sheet of plywood, a special delamination repair compound is injected through them with a syringe, the area is weighted down until it cures, and the holes are closed with plugs or filler.

These repair kits are sold by caravan accessory shops, each with its own instructions on hole spacing and curing time. It is a job an owner can do. Afterwards the floor is covered with new flooring and no trace is left.

Repairing a rotten area

Injection will not help here: there is nothing to bond.

• A small area. The damaged plywood is cut back to sound material, the cavity is dried, the insulation replaced, a new sheet glued in and the joint reinforced.
• A large area or a zone along the side. The floor is tied into the walls and the chassis. This is a job for a workshop that repairs caravans.

Everything must be dry before it is closed up. Moisture sealed inside will carry on working.

Can new flooring hide the problem?

No, and here is why.

• PVC does not let moisture through. Wet plywood under it stops drying from above and rots faster.
• Adhesive does not hold on a damp, crumbly base.
• A soft area will give under new flooring too.

The right order: leak, drying, repair of the base, and only then roll flooring. On a dry, firm floor, a continuous sheet with no seams is already working for you: water spilt inside stays on the surface and does not reach the plywood.

If you are deciding what to put on the camper floor — roll flooring, PVC tiles or laminate —, the comparison is in the article which flooring to choose for a campervan. And do not forget the weight: for campervans with a 3500 kg MMA limit, an extra layer can matter — more in campervan floor weight and the 3500 kg limit.

Winter storage

Most floor problems are picked up not on the road but in storage.

• Ventilation. Leave the ventilation grilles open. A sealed-up caravan collects condensation.
• Moisture absorbers. Put them in and replace them as they fill.
• Water. Drain the tanks, the boiler and the pipework.
• Soft furnishings. Stand mattresses and cushions on edge or take them home.
• Cover. Breathable only. Plastic sheeting or a tarpaulin without ventilation creates a greenhouse.
• Seals. Inspect windows, roof lights and seams before the rainy season.
• Inspection. Go in once a month: the smell of damp is obvious straight away.
• Floor. Do not leave rubber-backed mats on the floor: moisture collects under them, and dark rubber leaves stains on PVC.

When you need a workshop

• the soft zone runs along the side or is in a corner;
• the moisture meter shows damp over a large area;
• you cannot find the source of the water;
• the floor gives near the fixings of furniture or seats.

FAQ

How much does a caravan floor repair cost? It depends on the area and the cause. An owner can inject a small area for the price of a repair kit. Replacing a rotten section in a workshop is priced once it has been opened up.

Can I travel with a soft floor? Minor delamination in the walkway does not affect safety, but it will spread. Rot by the side wall or the seat fixings should be shown to a workshop before you travel.

How do I know the leak is fixed? After repairing the seals, follow the moisture meter readings over several rainy weeks. They should fall.

Should the floor be insulated during the repair? When a section is replaced, the insulation is reinstated at the same thickness. Changing the whole floor construction only makes sense in a full refurbishment.

The same logic applies in buildings: moisture from the base destroys the adhesive under any covering. More in vinyl in a basement: what to do about a damp subfloor.