Waterproofing plywood - trailer floor/deck use


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Established Member
10 Mar 2014
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Wiltshire Amesbury
Good evening all,

I recently bought a bit of a Lemon Ifor Williams flatbed trailer.
I did not spot half the problems it had when I bought it, and I definitely overpaid :(

I am replacing the bump stops, suspension bushes, and brake cables and re-doing all the electrics to name a few.
There is no point crying over split milk, and all I can do is fix the issues/replace the knackered parts, which bring me to the floor/deck of the trailer.
The floor was completely rotten (hidden by some aluminium treadplate) and it needs replacing now.



The perfect solution for the floor would be to buy some buffalo board / phenolic plywood BUT funds are tight with the extra expenses on the trailer and I have got some free 'normal' (not marine) plywood sheets I can use.
While I am fully aware that they will never last as long as the 'proper' stuff I do want to waterproof them/coat them with something which should give me a few years of use before I need to replace them.

What product could I use to waterproof the boards?
I am considering something like Everbuild 908 DPM or Everbuild 905 All Weather Roof Coating which can be bought for between £22 - £25 for 5 litres


The treadplate will go back on top of the plywood so the coating does not necessarily have to be hard-wearing/withstand normal trailer use.
Has anybody had any experience with those products or can suggest an alternative?

Thanks in advance!
As an alternative to those you show, which are bitumen based, maybe look at the equivalent ones that are resin polymer based (e.g. Everbuild Evercryl or Liquid Roof). If you prime the plywood with SBR before applying the membrane it wil help. Even something like a tanking product for a wetroom might work well (e.g. Waterproof Tanking Kit System WSK for Wetrooms, Bathrooms, Kitchens Wetrooms). Drizzle a bit in each screw hole before adding the screw and put a second coat at the joins between sheets.

It might help when storing the trailer either to cover the deck or raise one side up on a small ramp so it has a fall to it and any water from the sky runs off.

If you plan to replace in the future, choose screws that will be removable/reusable (i.e. not Tek screws).

Does it/will it have mudguards to slow down or contain road spray on the underside?
I would remove the plywood and replace the cross members with aluminium channel and put the aluminium deck sheet back on.
Could you use 22mm waterproof flooring chipboard? Depends on how it is supported by the trailer frame. I have a bit left over from a floor which I use as a flat surface for a small trolley jack on the gravel drive. When not in use it lives at the side of the workshop. Has been repeatedly soaked, frozen etc and still going strong after several years. Only used for changing wheels and such, little low profile toy Jack a lot easier to lug up the drive than the "proper" ones in the workshop.
My understanding is that when IW sell trailers with an aluminium check plate deck, this is laid on top of treated wood deck boards, running front to back, rather than on top of ply.
You can buy rebated, Keruing truck-flooring. It seems to be about £ 9.00 to £11.00 a linear metre for 140mm wide boards - if that is within budget.
If you have already got free plywood sheets you will obviously want to use that. The best plywood sealer is a clear, penetrating epoxy (CPES) which will make it incredibly durable and also strengthen the plywood. The lower viscosity the better as it will penetrate further. Just make sure that all edges are fully treated as well as the faces. Check out Smiths CPES
Make sure you treat the sides of the board especially if you use the Phenolic board. My daughter had the floor of her horse trailer "professionally" replaced with phenolic board, after a few years I had to replace it as it had rotted along the edges which had not been treated.
I use old engine oil it soaks in dries and does not come off on your clothes and costs nothing, I also use it on fencing and fence posts. Most garages will be glad to give it to you.
I use old engine oil it soaks in dries and does not come off on your clothes and costs nothing, I also use it on fencing and fence posts. Most garages will be glad to give it to you.
We have an old bench that has been used for automotive purposes and nothing is going to rot that!!