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further to mot and damp check


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Hi all.


in my last posting, I explained the after serious debate, the dealership agreed to do temporary patch and then arrange return to Tewkesbury fo "proper repairs".


Re investigating underside , I can now see that most likely ingress at rear could be rear nearside corner, where the external fibreglass skin extends below the level of the floor and leaves a 10 mm wide gap across the rear between the chassis cross member and the external skin.. I cannot see how the floor/skin junction is supposed to be sealed, except that there seems to be a loose rubber strip along the rear dressed down over the rear edge of the floor, and then the rear panel added tightly against this rubber.


it is not possible to see clearly whether this rear edge of the floor is sealed or simply a "tight fit".


Can anyone say if my guess regarding the "sealing"is correct, and suggest how better to properly seal rearwards of the chassis cross member..I am thinking of possibly injecting some expanding foam sealant into the gap , and then sealing between the lower edge of this foam and the external fibreglass skin...


the forward edge of the chassis cross member is sealed to the floor, but it is the rearward edge where to my mind water could get in and creep into the bottom edge of rear wall/floor junction..

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Without being able to see Tony, it is very difficult to say how, or even whether, additional sealing should be applied.


Classical timber construction generally favours leaving gaps in preference to trying to seal one piece of timber against another. The thinking is that when two pieces are joined, unless the joint is fully bonded with a waterproof glue, there will be a tendency for small gaps to be created into which water will be drawn by capillary attraction. Then, once in, the water permeates the wood, which stays damp creating the ideal conditions for rot spores to germinate.


By instead leaving deliberate gaps where members abut each other air is allowed to circulate and so any wetting is temporary as it can then dry off.


The underside of a motorhome is a rather different kettle of fish as its environment on a wet and usually dirty road involves fine spray, sand and grit, varying air pressure, and high air speeds.


Ideally, one would not use natural wood in a motorhome floor. Possibly marine ply - which is so resin impregnated it is virtually wood reinforced resin - but otherwise GRP sheet.


However, much ply is used, and is usually assembled into panels with softwood battens spacing two ply layers apart. Wall panels are likely to have been stood on top of the floor panels and screwed into position.


This already unsatisfactory construction is then coated with some kind of bitumenous compound, often seeming little more than a paint, and shielded from view by side skirts and rear bumpers etc, that are frequently screwed to the side/floor panels. These, IMO, tend to funnel the road wet and dirt into the areas where wall meets floor, but also to restrict airflow when the van is stationary so as to reduce the drying effect of normal air movement. Some sealants may be added to these joints, but being out of sight, they may not be that carefully applied.


Construction methods vary, and I'm generalising, so your van may be better put together than I'm describing.


If it were possible, I think I'd be more inclined to deal with the situation you describe, as I understand it, by attaching a cover plate (ideally a PVC angle section) to cover the gap, sealing it against the floor but leaving it unsealed against the rear "bumper". Not ideal, but it would leave the floor edges open to the air space, while the downstand leg of the angle should prevent water drawing up into the gap. Something like a 50 x 50 mm angle, if possible stuck (adhesive sealant, not glue), and not screwed, to the floor. However, whether that is practical in reality will inevitably depend on the way the rear of your van has been assembled.

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Thanks Brian.

I guess I cant explain in words but will try.. the chassis rear cross member is 2 inch approx square section and the floor section overhangs this member rearwards by approx 1/2 inch. The rear skin drops vertically past the floor and then curves round forward towards underside of cross member leaving a gap between the skin and the cross member approx 15mm, but apparently in contact with the floor edge.


The forward edge of the curved skin acts therefore as a scoop and will deflect any wet or muck up between the crossss member and skin straight into the skin/floor junction.. it is this junction which cannot be seen because ot the curved area..it isnt possible to see round the corner lying under the van, and the damp shows inside the van at the wall floor junction.

if the floor /skin junction was sealed (or at least the floor /rear wall junction/had been properly sealed during assembly, the water couldn get in....


my thought is to fill the gap with expanding foam and then seal the then visible lower edge of the new foam..hope this makes some sense..

You suggestion to close the gap with something like angle providing a drip edge, wouldnt prevent the scoop action of forward travel unless it too was sealed against the fibreglass skin.


Further thoughts necessary on my part, but dont think dealer is likely to be interested in doing a comprehensive fix under warranty...van is 2009 autocruise Stargazer.




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Think I understand better now Tony! However, two things occur to me. For the scoop you describe to function as you think, air must be getting out of that chamber somewhere. Otherwise, there would be no airflow to carry the moisture up as far as (I think) it has to go to reach the floor. If that is the case, then the edge of the floor should be dried equally quickly by the same airflow under dry conditions. Basically, you can't ram air into a closed box, even if it has an opening along one edge.


Again, without being able to see, impossible to say, but are you sure that damp is getting up from below (which would only be the case only when the van is driven in the wet), rather then getting down from above? I gain the impression that the lower, "bumper" and rear lights, section of the rear is a separate panel. I just wonder, but what is the chance that water gets past this and then runs down until it meets the point where the rear wall skin meets the floor? That junction would be out of sight but, depending on how the base of the rear wall skin has been trimmed, might possibly be where water comes into contact with the edge of the floor. If that were the case, it would tend to get wet every time it rains, rather than only when it is driven in the wet. Is this feasible?


I think I'd want to see what is revealed when the rear has been stripped out, before attacking that bit where the bottom of the moulding sweeps forward under the rear chassis member. Have you planned to visit their workshop once the start repairs? It might be a good idea if you can, as it would give you a chance to discuss the proposed repair with them, and possibly to question what they intend doing if you don't like it. After all, it's you van they're playing with!

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Guest Peter James
Brian Kirby - 2015-03-29 6:53 PM

Basically, you can't ram air into a closed box, even if it has an opening along one edge.

Not if its just air. But what if its like a water jet thrown up from the tyres?

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Just taken a couple of pics of rear corner underside. Will try attaching images.. it might explain a bit better



1 shows the gap behind cross member

2 it the rubber sheet inner lining of rear panel

3 is temporary sealing attempt from corner to cross member.. cant get behind cross member


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That's much better Tony! :-) So, the black area outside the chassis frame is the ply underside of the floor, with whatever waterproofing was applied (i.e. basically, painted ply), and the area where the white temporary seal is would be more or less dead in line with the rear wheels. I hadn't visualised that, though Peter obviously had. Well done that man!


Where, in relationship to all that, is the damp?


Is the area inside the chassis frame, that appears brown in colour, really just untreated ply, as it seems to be?


I think I'd be inclined to attach a piece of 75mm x 75mm PVC or similar angle or channel to the underside of the painted ply so that it continues the line of the chassis cross member out to the side skirt. That would prevent direct spray hitting the rear wall/floor joint, and give it a slightly better chance of avoiding the water thrown off the rear tyres. I think I'd also consider rear mudflaps - unless there already are some. On a really wet road that area must get the equivalent of being hosed with a dirty water!


To make a good job of that joint they really need to remove the lower portion of the rear wall, clean off whatever sealant was there originally, and re-fit the wall to the floor with a new bead of sealant.


Having done all that, I think I'd then try applying some Finegans Waxoyl fairly liberally to the whole of the exposed ply area so as to reduce its tendency to absorb moisture. But, I also think I'd give some thought to selling the van, and looking for another that is rather better constructed.

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hi again, a couple more pics




Nearside Wheel Arch pic 1


1 Shows 3 Missing Screw Fixing Points,, Originally no screws so damp could penetrate here and creep forward into underseat side wall and back behind Fridge

2 Shows missing seal further to rear of wheel arch along inboard edge


Damp gets in somehwere along these edges and is detected behind fridge and in nearside under seat forward of wheel arch


and damp again below kitchen ie along lower edge of rear wall.


Re option to sell...maybe forced on me health wise.. doc appointment 16 45pm



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I'm think reason says don't try tackle this yourself, Tony. You have damp forward of, and behind, the nearside wheel arch, possibly due to more than one cause. There is no real telling, even from your extra photos, exactly where water is getting in, or for how long this has been happening, so it is possible there may be rotten timber to remove, as well as re-sealing the areas of leakage. If timber has to be cut out and removed, parts of the kitchen units and possibly appliances may also have to come out to gain access, and/or the nearside locker forward of the fridge may need to be removed, possibly the fridge and its cabinet as well. I'm deliberately trying to paint the worst case picture here, there is every chance it won't be that bad - but I'm in "prepare for the worst and hope for the best mode" here!


Trying to sell with the van showing damp will cost you dear, and trying to do the work yourself just might develop to nightmare proportions.


So, a suggestion. The Caravan Club has a new inspection service in conjunction with the Mobile Caravan Engineers Association. They have a website at www.caravaninspectors.co.uk tel: 01249 654992, e-mail services@caravaninspectors.co.uk. Try contacting them (motorhomes as well as trailer caravans), explain the circumstances and see if they can a) visit you to inspect the problem areas and see if they can reach any conclusion as to what is going on, and prepare a brief report. Submit that to Marquis in support of the necessity to have the work done. While in contact with Caravan Inspectors, as you don't now trust Marquis's workmanship, ask them b) if they would also follow up at Marquis Tewksbury on your behalf, while the repairs are under way. Maybe two visits, one to view the extent of damage and discuss remedials, and a final to inspect the job near completion.


I have no idea of the costs (or even if they will provide that kind of relatively bespoke service, but providing they get paid for the time, I can't see why they would turn it down), but it seems to me it may be worth asking. At least that should get you something approaching independent, professional, advice, plus some control over the proceedings, without having to worry over what Marquis are doing and how they are doing it. Maybe ending with a final inspection after repairs are complete, to sign-off? So, some (as yet unknown) expense, but the whole issue potentially out of your hair until the job is completed.


Marquis may object to a third party inspector attending, but they really should not, and it seems to me that they'd have shaky grounds for doing so. You are their customer, the van is yours, and they are working on it. The warranty, I assume, is insurance backed, so the insurer is paying, and insurers seem often to ask their insured to sign that they are satisfied with the standard of work executed. So, they may even welcome an independent inspection as evidence that their money has been wisely used. Who knows? :-)


Then, when the van is back repaired and in sound condition, it can be kept, sold, or traded at your discretion, in good condition, while maintaining its full potential value. Any use?


I hope the doc found nothing to add to your concerns. All the best.

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