DEALING WITH DAMP

The 'D' word probably strikes more fear into the heart of the average caravan or motorhome owner than any other. If left unchecked for any length of time damp can be very time consuming and costly to rectify. Here we look at the main causes of damp, how to avoid them and what to do if the worst happens

Main Causes Of Damp

Water ingress
Modern caravans are a marvel in terms of the facilities they offer for the size and weight. The downside of this is that that they cannot be made as rigid as, for example, a car. The welded steel construction of the car is replaced by lightweight materials bonded by special glues and mastics. These lightweight materials include aluminium, wood and various plastics. The problem with joining these materials is that they each expand and contract at different rates and so the integrity of the mastic is very important. The stresses imposed by towing, especially over bumpy roads, can  also induce joint stresses.  New mastic will not retain its elasticity forever and eventually it will become brittle and fail. The factors governing its life include weather exposure, mastic type, degree of flexing and how well it has bonded to the joint surfaces. Once the mastic has begun to fail, or indeed if it was not adequately applied in the first place, then water penetration is likely to begin.  

Prolonged hot weather is well known for inducing mastic failure, so do be mindful if taking an older van to the continent for a few weeks in the summer.

Faulty plumbing This is more common than you might think and often goes unnoticed. Faulty joints, frost damaged components and cracked sinks can all produce insidious leaks which, over time, can lead to significant damp problems. They tend to go unnoticed not just because of their insidious nature but also because the damp can build up behind floor and wall coverings without being noticed. For this reason it's always worth giving the system a good check over once or twice per year.

Spillages
Most of us christen our vans in this way from time to time. We might think we've mopped it all up but if a significant amount has been spilled then some may have found its way underneath floor coverings and out of sight. On emptying the van one autumn I found a can of fizzy drink which had rolled into the corner of  a bed bunk and had obviously been there some time. When I came to remove it I found it was all but empty. This was strange because it had never been opened. Closer inspection revealed a minute puncture mark, presumably caused by the can rolling round a little for mile after mile in transit. The vinyl floor covering was totally dry so I was hopeful that no damp had been caused. The damp meter told a different story. Several square feet of floor covering had to be lifted and the floor took a couple of weeks to dry properly.

Condensation
Condensation forms when air is cooled to the point where it can no longer hold all the moisture trapped within it. The main problems occur during the colder months when a spell of cold weather is followed by a spell of warmer moist weather. The warmer air within the van meets the cold surfaces inside the van and moisture is deposited. Favourite places for this are the inside corners of the van and in closed cupboards. The best way of avoiding it is to ensure that the van has adequate ventilation. This means checking that all vents are clean and unobscured and leaving cupboards and bunks open so that air can circulate. 

Avoiding Damp Problems

Inspecting and testing for damp
The best way to minimise the effects of damp are to catch it early and that means a thorough inspection and professional damp test at least once a year. The damp test is normally carried out during the annual service but even if you do your own servicing it's still vital to get a professional check done. Beware that the damp meters found in DIY stores are generally not as accurate as professional types and can never replace them.  It's also important that the person doing the damp check has been properly trained in terms of where to look and how to avoid false readings.

In-between damp tests it's worth checking around all seams for evidence of the mastic drying out. Pay particular attention to horizontal seams such as awning rails, window hangars, roof to body seams and body to body seams. Other known trouble spots include window frame seals, awning channel rails, and grab handles (are they still solidly attached?).

External light fittings such as repeater lights and awning lights can also be a source of water ingress. These fittings are normally fed from behind via a sealed hole in the bodywork  and sit on a neoprene gasket. If the fitting or gasket appear loose or in poor condition this could be sign of trouble.

The damaged area in this photo has probably been caused by a leak involving the front offside repeater light

Any signs of water penetration must be treated immediately before any lasting damage is done.

In damp weather look for sign of water disappearing behind horizontal trip strips and not reappearing underneath. If this happens then the water is almost certainly finding its way into the structure of the van.

Periodic resealing
It is good practice for awning rails and trim strips to be removed and resealed every at least once every 5 years.

Storage Considerations

If you have the opportunity of storing your van in the sun or the shade, consider choosing the shade. Under cover storage is obviously best but avoid heated storage.

Drying Out

If your van does get damp then the most efficient way to dry it out is with a dehumidifier. These uses far less power than heating with the added bonus (for unattended operation) that they present very little fire risk. If a dehumidifier is not a viable option then the alternatives are ventilation and heating. One of the best times to dry  a van out using heat is during very cold weather. This is because very cold air contains hardly any moisture so when you heat it, it can absorb large amounts. The downside to this is that you need to ensure sufficient ventilation to stop the newly-absorbed moisture condensing in the cooler areas of the van.

Where moisture becomes trapped behind non-porous surfaces which cannot easily be lifted or removed then drying out can be a real problem. There are special techniques which can sometimes be used but often the van will have to be partially stripped to expose the damp areas and thereby enable them to dry. One trick for drying out plastic coated wallboards which have become a little damp is to make the surface breathable by piercing it gently with a pin to produce hundreds of very tiny (i.e. virtually invisible) holes.

If you do suspect a problem, and your caravan is still under guarantee, then take it back to the supplying dealer as soon as possible for a thorough check. Where the supplying dealer is at the other end of the country contact Swift for the name of a dealer nearer to you who will undertake any warranty work.

If your caravan is out of guarantee then pop it along to a reputable workshop to get their advice and a quotation. Try to obtain quotations from at least two other workshops before placing an order.

Should you feel like tackling the problem yourself then be prepared to be both thorough and ruthless. Anything less and you'll be wasting your time! Remember that the source of a leak can be some distance from the damp area and that water can travel horizontally along internal support battens.

If you think the picture on the left looks bad enough the picture on the right shows the same area after removal of the front nearside bed box! Clearly the problem stems from the window sealing and could have been present for two years or more.  Beyond the scope of DIY repair? Not so, thought the owner of this van who effected a good repair!

One of the most straightforward DIY jobs is the resealing of trims and awning rails. These are bedded onto mastic and fixed by means of stainless steel screws (normally covered by a removable plastic trim strip). Having removed the screws carefully ease back the metal strip a little at a time until it is completely free. Next remove all traces of the old sealant, then clean up the mating surfaces and degrease them. The most suitable degreasing agent is isopropyl alcohol which you may be able to get from a chemist or caravan workshop.

Once everything's spotless you can apply the new mastic. Be sure to use a  good quality non-drying bedding sealant. These can be often be obtained in either cartridge or tape form. Tape as is easier to apply and gives an even coating. (Suitable  products include Sikaflex 512, Carafax IDL 99 and Hodgsons Seamseal CV.) Offer up the metal strip and gently push it onto the mastic so that the mastic oozes through the screw holes. Replace the screws tightening evenly until the mastic begins to be squeezed out from the sides. Finally, remove all surplus mastic and replace the plastic trim. If any screws refuse to bite on reinsertion it could be that the wood into which you are driving them is soft through damp. You can try longer screws but be careful they don't protrude through to the inside of the van.