# Undersealing



## GMJ (Jun 24, 2014)

Hi


My Bess E795 has some boards underneath right at the rear end, that are starting to throw their screws. Where this is because of buckling or because they have been disturbed (tow bar or reverse sensors cabling) I don't know.


Any way I plan to refix them with a line of screws (screws are already there holding the boards) and then apply a sealer of some kind. Im thinking waxoyl but am open to suggestions.


It looks as though the boards have been treated some time in the past with a black substance hence my thoughts of waxoyl.


Any other suggestions folks?


Cheers


Graham:smile2:


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## GMJ (Jun 24, 2014)

Update (on advice received from the Swift forum just in case anyone does a search in the future on this subject)


A chap from Swift suggested pre drilling holes; putting some sealant into the holes and then screwing in making sure to keep near the outside of the boards as there would be a timber frame underneath to screw into. He suggested NOT to use any underseal as the boards were high spec marine grade and any sealant on them would inhibit moisture getting out of the boards if present. 


He also explained that the black covering on them was just a staining rather than an underseal.


Therefore I think I'll give it a go - weather permitting - on Friday prior to our jaunt up to Scotland.


Graham:smile2:


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## GMJ (Jun 24, 2014)

Update


I had a go at this on Friday with some mixed results.


I predrilled the holes however I couldn't get the screws to bite properly into the board underneath (too short screws; or too big a hole I guess; or the boards are too far apart). Anyhow, no worries: I nipped some sealant into the screw holes prior to screwing and applied a bead to the join where the boards overlap.


When I get her back in 2 weeks I'll put some larger screws in and get some more waterproof mastic/sealant just to make the join watertight....provided its nice and dry that it


Graham:smile2:


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## Poulbot (Nov 8, 2013)

I saw on another thread that the black paint applied to the underside of motorhomes these days is a breathable moisture repellant, so would agree that underseal is not advisable. Sounds as though you have got the rest of the problem pretty much sorted!


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## Spacerunner (Mar 18, 2006)

I'm working underneath my motorhome at the moment due to water damage. It appears that over the last 7 years the water that runs down the rear wall and goes between the wall and bumper gets into the wall through both the wallboard and micro flaws in the underseal.
The underseal is definitely not permeable as there was water dripping through the probe holes I had made and the wood was not drying. So I took a wire brush to it and scoured off the underseal and the wood is starting to dry quite quickly.
I've removed all the soft wood and the next job is to whack plenty of Ronseal wood hardener on it. Then fill any cavities with Ronseals high performance wood filler.
After that a coat of flexible wood primer and undercoat followed by a coat or two of Ronseal's 10 year weatherproof exterior black paint.


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## GMJ (Jun 24, 2014)

It does seem like very old technology for such an expensive outlay really doesn't it? Wood construction? I know its marine grade but still...Wooden boards underneath where all the surface water gets thrown about!


Graham:surprise:


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## Spacerunner (Mar 18, 2006)

GMJ said:


> It does seem like very old technology for such an expensive outlay really doesn't it? Wood construction? I know its marine grade but still...Wooden boards underneath where all the surface water gets thrown about!
> 
> Graham:surprise:


Totally agree. I'd like to see some sort of honeycomb resin construction.
When you really start to examine the underneath construction it makes you wonder how it stands up to six month use never alone six years.


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## GMJ (Jun 24, 2014)

*Update*

Job jobbed!:grin2:

I got some size 12 screws, 1.5 inch I think plus some waterproof, flexible mastic. A blob of mastic in each hole; screws popped in and biting; then several good lines of mastic at the wood edge followed each time by my finger pushing it into the join.

Cost: £7.50 and a bit of time/leccy. Garage quoted 5 hours labour at 50odd quid an hour plus VAT:surprise: plus a tin of sealant! (which shouldn't be used anyway!):surprise:

I'll keep an eye on it over time just to check.

Graham:smile2:


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## coppo (May 27, 2009)

GMJ said:


> Job jobbed!:grin2:
> 
> I got some size 12 screws, 1.5 inch I think plus some waterproof, flexible mastic. A blob of mastic in each hole; screws popped in and biting; then several good lines of mastic at the wood edge followed each time by my finger pushing it into the join.
> 
> ...


Good job, just make sure the screws are not so long that that they go into a pipe or something.

Paul.


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## GMJ (Jun 24, 2014)

Thanks Paul


The existing ones are 1.25 in length so I gambled on the extra .25 but the point you make is very valid: that could be messy :surprise:


Graham:smile2:


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## coppo (May 27, 2009)

GMJ said:


> Thanks Paul
> 
> The existing ones are 1.25 in length so I gambled on the extra .25 but the point you make is very valid: that could be messy :surprise:
> 
> Graham:smile2:


Yes it could, I remember a that guy Clive Mott who writes for MMM, was working on his Concorde and drilled right through the water tank from underneath.

Paul.


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## GMJ (Jun 24, 2014)

Oops!:surprise:


I didn't notice any puddles or water loss over the weekend so hopefully Iv got away with it:grin2:


Graham:smile2:


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