I'm fixing a rough old trailer (8.5'x4.5') and need to replace the base. I am planning to get a couple of sheets of WBP plywood, probably 18mm thick. It seems to be referred to as "Shuttering" grade ply. I am hoping to get the wood for around £20/sheet.
The trailer will normally be left in the open, without a cover, parked tilted so it drains. So it will definitely get wet! Any suggestions as to:
- the choice of wood (plywood, grade, thickness)?
- how to treat/protect the wood to give it a few years life (creosote, paint, varnish, etc)
I'm not sure if it's the 'right' answer - but I converted a caravan chassis (£20!) into a ridiculously large 'collecting firewood' trailer by doing a 'cut and shut' on the steel chassis. I then built a shallow box of 18mm shuttering ply on top of the chassis
- with 3 x 2 uprights at the corners, bolted inside the chassis corners. Some 3 x 1 bolted along the top edges helped to stiffen it all up.
Some bits & pieces from Towsure gave me a drop-down / removable tailgate
- and some of their 'cage-protected' lighing clusters made it vaguely street-legal.
Luckily the old chassis had 'real' suspension with leaf-springs - although I _should_ have allowed for the vertical deflection caused by the weight of a tonne or so of firewood when constructing the wheel-arches - as the first time she was loaded up the tyres rubbed on the inner wheel arches and produced plumes of black 'dragster smoke'.. very impressive - but expensive on the tyres!
I 'treated' the timber with some black 'shed' treatment - because that's what I had 'spare'. After four years sitting outside in all weathers there was no noticeable deterioration in the timber. On reflection, it might have been a good idea to cover the cut edges of the shuttering ply with a lip of 2 x 1 well masticed on - as there were a fair few voids in the ply and that's likely to be where water would get in and cause problems...
The trailer wouldn't win any design awards - and never ventured more than about 15 miles from home - but she was great for trotting around the local forestry tracks collecting firewood....
Dear Steve WBP is correct rather than shuttering For "treatment" it is best to think - "make water resistant" - to this end I suggest a water repellant preservative stain on the upper surfaces or best before you put it in on top and bottom surfaces. for the edges - especially any cut edges it is worth treating as you will have some form of exposed end grain To this end (npi) use a polythene "dip tank" and an organic solvent preservative with a fungicide and dip it overnight allow to dry seal end grain with heavy metal primer paint to "refusal" and then apply (as suggested above) a mastic or the like
leave outside such that water can drain off and wind can get at it
Should then see a good few years of service
You will have to reapply WRPS every couple of years or so
There is a type of resin-faced shuttering plywood which is extremely durable. It is normally used to give an particularly smooth finish to in-situ concrete, but the resin also gives it exceptional longevity.
It sells under the "Wisaform" brand (pronounced 'wiser form') and, when I last bought some, it cost about double the price of normal shuttering plywood. But you save the time and expense of treating it, except that obviously you still need to treat the cut edges. The resin finish is dark brown in colour.
It is some years since I bought Wisaform but I have seen resin-faced plywood in use very recently. There may be other brands. I feel sure that a good timber merchant, preferably one who specialises in plywood, would easily be able to source it.
WBP is a hell of a price. I use spruce shuttering ply for everything these days, even replacing much of my expensive birch furniture-grade. The "cheap" I've been buying is pretty good (8 / 10 sheets have good surfaces) and the birch gets worse the more I pay for it. This is from Avon Plywood in Keynsham.
Even if you have to replace cheap shuttering every few years, it's still cheaper than WBP. If you paint it though, spruce shuttering lasts pretty well.
If you can get some old T&G floorboards, they will make a lighter thicker base. As has been suggested unless you are planning on keeping the trailer for a long time, the cheapest solution, with plenty of paint on the edges is probably best value.
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