Damp ingress through the roof

[Troyboy]

Having owned and lived on a few yachts (one 40 footer which I built myself - took 9 years of hard graft),

I am aware that many camper problems are the same as leaking deck problems on a boat.

Having just a bought a P reg Hymer B544 which at the moment appears dry, I have to say that because Hymer use a layer of theoretically closed cell foam behind the GRP and the aluminium sheets which make up the coach house, leaks into the interior are less problematic than leaks into the foam (which obviously take place at the same time). Such leaks in a closed cell foam deck are seriously bad news and the water will eventually soften and even destroy the foam completely causing the deck to sag. The repair is long hard and costly (even when one does it oneself). Caught at the outset (in a motor home) the foam will eventually dry (its much thinner than a foam deck) but if its an old leak the foam will have wicked the water many yards from the leak.

 

Someone has suggested using a quality chlorinated rubber style paint (similar to deck paint). Its a good idea if applied with consummate skill and matches the general appearance of the vehicle. Otherwise find that leak at breakneck speed. Its working its wicked wicking as we speak. :-(

[Dave Newell]

How does water "wick" through closed cell foam? I thought the whole point of closed cell foam was that each "cell" is closed and so moisture connat transfer from cell to cell, i.e. its waterproof. Have I misunderstood the concept of closed cell foam?

 

D.

[Brian Kirby]

The foam fill Hymer use in their PUAL construction is stated by Hymer to be, in simple terms, impervious to water. If the cell membrane were water permeable, even if the cells were closed, water would eventually be absorbed, but Hymer claim theirs is not. Short of defective assembly, I think Troyboy is worrying unnecessarily.

[globebuster]

As with all products, there are variations in quality, but no CCF is a poor performer.

 

Divinycell DIAB is probably recognised as the best [inert gas filled] this is probably why old Hymers outlast a lot of other makes - their PUAL concept has been around ages.

 

I won't bore you with Thermal Indifference and other factors, but ironically thicker Polysterene foams will exacerbate the build up of moisture hence so many old british built vans are corroding from the inside out 'peppering' the aluminium substrate - roofs predominantly. Moisture almost certainly won't broach cheaper insulation either [unless there is a leak] but will certainly condense and store considerably more.

 

Closed cell foam should never absorb moisture, even when damaged.

 

However there is a very exact science when it comes to insulation, inferior thicker materials are no match for a good quality base product, that may appear to the layman as too thin giving the perception of being less capable.

 

Trust me, I know a bit about this subject.