Newcomers seeking advice GRP delamination?

[MikeEB]

Thanks for accepting us onto your forum.

We are complete novices to motorhomes and decided to dip a toe and look for a vehicle with a budget below £15k. Really can’t stretch beyond that in current times which means we are pretty restricted and focussing on private ads in the main. It is a jungle out there folks!

The reason for this post is to ask for advice regarding delamination of GRP panels. We are smitten with a 2001 two berth Auto Cruise Wentworth which is immaculate and dry inside and rock solid underneath, but…there are areas of quite large blisters on the outer GRP skin above the side windows and forward of the habitation door below the retaining catch. The ‘blisters’ are rigid but unsightly.

 

Should we completely avoid vehicles with this problem? Is it repairable? Is it just a fact of life with a 20 year old vehicle?

 

An acquaintance who is a boat builder told us that they regularly repair similar issues on boats by drilling the ‘bubble’ from the outside, injecting a specialist filler/hardener into the cavity and then belt sanding it back to the original profile. Sounds plausible but some advice would be very welcome.

 

[BruceM]

I used to own a GRP hulled boat and indeed what you describe does sound a bit like a case of what in this part of the country we tended to call GRP pox, or alternatively by it’s proper name of GRP Osmosis (see here https://www.makewoodgood.co.uk/causes-of-osmosis-blistering-grp/ ). I’m surprised that it’s occurring in the relatively dry environment of a land based vehicle but then I guess depending on the quality of the construction it’s possible. You mention that the blistering is large but you do not say how large. Certainly it indicates an issue either with the original construction quality or if really caused by GRP Osmosis, water. As it’s an older vehicle I’d suggest it’s worth budgeting a couple of thousand pounds for repairs/enhancements anyway so as you’ve now identified a defect I’d suggest you have it run along to a GRP body repair shop to see what they’d charge for the repair and renegotiate the price accordingly.

[mikefitz]

As suggested the blisters are the result of osmosis and the resultant pressure build up usually between the protective gel coat and the GRP layup. The problem rarely effects the strength of the GRP structure and the usual treatment is to grind off the gel coat in the effected area, clean, ( there is usually an unpleasant liquid in the blister), allow to dry. The finish is restored with gelcoat for small blisters whilst larger are filled with two part epoxy filler before the gelcoat finish.

https://www.ecfibreglasssupplies.co.uk/product/gelcoat-repair-kit-1-white

https://www.amazon.co.uk/PC-11-Marine-Waterproof-Underwater-Repairs/dp/B000LNOJW6/ref=sr_1_7?dchild=1&keywords=marine+two+pack+Epoxy+Filler&qid=1593438720&sr=8-7

If the problem is localized then its worth repairing but if there are significant areas with blisters it suggests that the original GRP layup was in some way faulty and the problem may be ongoing.

Although time consuming the repair is a fairly easy DIY task.

 

Mike

 

 

 

[mikejkay]

BruceM - 2020-06-29 2:32 PM

 

I used to own a GRP hulled boat and indeed what you describe does sound a bit like a case of what in this part of the country we tended to call GRP pox, or alternatively by it’s proper name of GRP Osmosis (see here https://www.makewoodgood.co.uk/causes-of-osmosis-blistering-grp/ ). I’m surprised that it’s occurring in the relatively dry environment of a land based vehicle but then I guess depending on the quality of the construction it’s possible. You mention that the blistering is large but you do not say how large. Certainly it indicates an issue either with the original construction quality or if really caused by GRP Osmosis, water. As it’s an older vehicle I’d suggest it’s worth budgeting a couple of thousand pounds for repairs/enhancements anyway so as you’ve now identified a defect I’d suggest you have it run along to a GRP body repair shop to see what they’d charge for the repair and renegotiate the price accordingly.

 

If it is boat pox the blisters will be filled with a fluid which has a very distinctive odour. The blisters are due to air bubbles in a poor quality gel coat that become filled with water that leaches out chemicals in the galss fibre. From my experience, with boats, the blisters are small and not hard. A pinprick will release fluid, if it's there, and you can check the smell.

On my boat I sanded out the blisters, washed the hull thoroughly and painted with a two part epoxy. The problem was largely underwater and out of sight so therefore not too much of a problem. On a motorhome it will be different.

Probable best to remove the blistered material and redo the gel coat. A specialist fibreglass car repairer could to the job.

One thing. I had a patch of blisters on the coachroof where a lifebelt was kept. Water had been trapped

 

[MikeEB]

Thanks for responses, if it helps to clarify, these blisters are not soft in any way and retain the same finish as the surrounding panel, They vary from a couple of cms to about 10cms in diameter and are about 1 cm high.

[globebuster]

I very much doubt it's osmosis, unless the lay-up was done in the rain, or there is water ingress you are not aware of.

 

As you alluded to, it will probably just be delamination

 

Assuming it's a bonded foam sandwich, it will be the GRP skin 'letting go' from the foam substrate.

 

If it's above the window or adjacent to a fitting, the possible over compression during installation will 'load up' the surrounding area, causing a delamination in the bond - possibly combined with a bit of solvent entrapment.

 

I doubt that it will effect the integrity of the construction, and your boat builder guy is right - although I'd steer clear of a belt sander!

If you can live with it, I'd leave well alone and monitor it in the short term.

 

I would imagine your observation will make an excellent tool to negotiate a favourable price though!

 

 

 

[MikeEB]

Thank you Globebuster. I view the fact that these 'bubbles' are rigid as something of a positive. They are a little unsightly but the MH is nearly 20 years old. My main concern was that this may be a common problem with older GRP panels and, as newcomers, we were on the verge of making a costly error by accepting a well known and potentially terminal issue. In view of the absence of advice to run for the hills or don't touch it with a bargepole I am inclined to take the advice and negotiate a better price.

[kevina]

globebuster - 2020-06-29 6:01 PM

 

I very much doubt it's osmosis, unless the lay-up was done in the rain, or there is water ingress you are not aware of.

 

As you alluded to, it will probably just be delamination

 

Assuming it's a bonded foam sandwich, it will be the GRP skin 'letting go' from the foam substrate.

 

If it's above the window or adjacent to a fitting, the possible over compression during installation will 'load up' the surrounding area, causing a delamination in the bond - possibly combined with a bit of solvent entrapment.

 

I doubt that it will effect the integrity of the construction, and your boat builder guy is right - although I'd steer clear of a belt sander!

If you can live with it, I'd leave well alone and monitor it in the short term.

 

I would imagine your observation will make an excellent tool to negotiate a favourable price though!

 

 

 

This. I used to manufacture grp products on a foam core and this is an air pocket, although you could drill holes to inject resin and rebond it probably won't improve the longevity but will also not improve cosmetics. Leave well alone and keep away ftom "expert" repairers, especially those with belt sanders!

 

The only thing worth doing is to park it with the blisters away from hot sun, if the foam core is polyurethane it will contain blowing agents which will get released from the mini foam bubbles the more the blister spreads - so it is a sort oc ongoing thing.

 

Is the grp coloured? I ask because coloured grp will get a lot hotter than white and so be more prone to this

[MikeEB]

Thanks Kevina, that fits well with the fact that the outer skin is still rigid with no cracks or splits and presumably expanded with the help of heat to soften the outer layer. I assume GRP has no way of shrinking back and it cooled as a rigid bubble. As the problem is on both side panels keeeping them out of hot sunlight would be virtually impossible.

[Derek Uzzell]

MikeEB - 2020-06-29 4:56 PM

 

...They vary from a couple of cms to about 10cms in diameter and are about 1 cm high.

 

This isn’t ‘normal' for an Autocruise Wentworth - or any motorhome with GRP-skinned body panels for that matter.

 

The fault won’t get any better on its own and may well get much worse.

 

As you are a complete novice to motorhomes, you’d be wise to walk away from this one.

[MikeEB]

Thank you Derek Uzzell, the fact that this isn't 'normal' has to be the deciding factor as we are complete novices. Many thanks to all who took the time and trouble to respond. On with the search.

[Cruisecontrol]

Hopefully just slightly off topic, but certainly referring to an Auto Cruise Wentworth.

 

In 2012 we owned a 2007 Wentworth for about a year - lovely van but found that both outside locker doors (under bed compartments) suffered damp. Both were repaired satisfactorily by the dealer under warranty. The dealer maintained, and I have no reason to doubt him, that the water ingress found its way in via the joint in the decorative aluminium strip surround. I subsequently checked other Wentworths at shows (Newbury etc) and found similar problems. That said - in other respects they are lovely motor homes.