Sealing under floor woodwork

[MagHal]

Hi I'm new to these for a and to motorhome ownership.

 

I'm due to drop the waste tank on my Avantgarde over winter to replace a level float switch.

 

This gives me opportunity to clean up metal work and Waxoyl the chassis. I was wondering however about wood treatment. Does anyone have any experience or recommendations about treating ply? I thought an antifungal preservative or repellent like Thompsons water seal would be Ok but I know some people are against sealing in case it seals in damp. Glad of any opinions.

 

Hal

[Mickt]

I am interested in this has nobody got a reply

[Derek Uzzell]

A GOOGLE-search usng “motorhome sealing plywood” as the search term will retrieve information/discussion that should be helpful. For example

 

http://www.caravantalk.co.uk/community/topic/53822-underfloor-sealer/

 

Although Thompson’s “Water Seal” is strongly recommended in the CaravanTalk discussion, consulting Thompson’s own website reveals the statement “Compatibility - Not suitable for plywood”. No explanation is given, but there may be the possibility that the product would harm the plywood’s glue interlayering.

 

To a large extent what product is best used to treat Hal’s motorhome’s floor is going to depend on what (if anything) is already on the plywood and what condition the plywood is in. Any ‘rot’ found will need to be addressed and it would be decidedly risky to use a traditional ‘underseal’ as this would tend to trap damp in the wood.

 

If I were going to spray Waxoyl on the chassis (a horrid DIY job unless one has access to suitably heavy-duty lifting equipment) I think I’d just spray the underside of the plywood floor with Waxoyl as well, rather than use a different product.

 

Dunno really - it might be a good idea to ask some of the companies that offer motorhome rustproofing services what they use if the customer wants a plywood floor treated.

[MagHal]

Thanks, sounds like few if any have tried it and the possibility of a solvent based water proofer delaminating the ply is something I hadn't thought of.

 

My van is in really good condition underneath. At 8 years old it has only 11K on the clock and the chassis is still clean and white, some minor surface rust in a few places. The floor looks dry and solid so a surface coat to repel water might be all it needs. Waxoyl is probably as good as anything.

 

I'll keep looking and let you all know.

 

Cheers Hal

[MagHal]

I'm giving up on this one.

 

All the reading I've done indicates it isn't a good idea. CPES looked promising but it's expensive and degraded by UV. Painting over it would prevent moisture from drying out.

 

I think its best left alone.

 

Cheers Hal

[Billggski]

Just a point to consider, 11K in 8 years means the MH has been standing around for most of its life.

Motors like being used, like us oldies we get stiff and cranky if in one place for too long, so things like tyres, cam belts, engine oil and so on deteriorate quicker than a high mileage model.

The floor probably hadn't had any exposure to road salt and muck, under seal can trap moisture in rather than repel it, in the past I have had cars where the underseal was holding the floor together as the steel had rusted away.

Waxoyl is quite pungent and it is recommended not to sleep in the vehicle for a while after treatment, some prefer Dynatrol, others used engine oil, but on the metal bits not the wood.

[MagHal]

Thanks for that.

 

I had the oil, cam belt, tensioner kit and water pump replaced as soon as I'd bought it and it had 12 months new MOT. You're quite right, these things need replacing even on a standing van.

 

I've since put nearly 1K on the clock and its running fine. Just the odd niggle with O rings on plumbing and a stuck level sensor (now repaired).

 

I'm waxoyling the chassis and laying it up for the winter.

[Billggski]

Sounds like you know what you're doing, but check the age of the tyres. A four figure number, month and year eg. 1114 would be this month. If they are the originals, consider replacement.

[Steve928]

I used to use a water seal product on my Elddis underfloor.

The van's usage was a bit different to yours though as we would cover your 8 year mileage total in an average year and continued to use the van right through winter out on the wet and salty roads. Furthermore we live out in the sticks and the last 3 or 4 miles home are on dirty country lanes, passing farmyards and wooded areas, then down our bumpy potholed track for the last half mile. The underside of the van got wet and muddy on every single trip.

 

I applied water seal liberally at least twice a year and felt that it did a really good job. Without it the floor stayed permanently wet and muddy. With it the water just beaded and dried off quickly and the mud fell off.

 

I say 'a water seal product' because Thomson's Water Seal is not what it used to be; it went VOC free and water-based (yes, really, a water-based waterproofer..) a couple of years back and now resembles thin milk. I still have a 5 litre can of it and haven't been able to identify anything that it's good for. Thankfully other manufacturers still make the 'traditional' water seal, solvent-based and silicone-rich. Examples are Wickes and Screwfix.

 

I didn't notice any warnings about use on plywood and certainly didn't encounter any such problems over 4 years.