Difference in plywoods

[JimM]

Guys, I need to get some plywood to refurb my trailer, it's only for the sides so thinking 12mm will be plenty thick enough but looking at the Wickes site they do 2 types in the 8'x4' sheets. The first is described as exterior plywood

the other structural plywood

both appear to meet the same standards and the descriptions imply that both can be used externally so is the only difference going to be that the structural won't have as good a finish veneer as the exterior grade ? Given that I'm going to paint all the surfaces anyway would there be any benefit buying the more expensive stuff (I know it's only £5 more but that's the kids fed for another couple of days :)

Cheers

Jim

[Grimly Curmudgeon]

For a trailer, unless you're really concerned about appearance, shuttering or structural ply is fine. It will be slightly rougher in finish, but easily covered with paint. You also get more voids in it, but it will last years anyway if you soak it with creosote or similar.

[harryagain]

Ideal is marine ply. (If you can afford it.)

[dennis]

8<

I did my trailer using 1/2" shuttering ply and gave it a coat of fencelife (it wasn't called that but it was similar water based stuff) about 30 years ago. The timber lasted 20 years, the chassis didn't, probably due to it being stored outside in the weather.

[Baz]

Have you considered

[Rick Hughes]

I would disagree here ... you need WBP based Ply on a trailer .. or it will not stand wet or damp. Not all structural ply is WBP.

WBP .. means it has water proof glue holding laminations together. The grades like BB or similar been the quality of face .. A= best no knots etc. Most plys have one face 'better' than other.

A BB or WG grade would suit a trailer as long as it is WBP rated glued

All you need to know can be found on line in seconds ... here is one such link:

[fred]

r grade ? Given

be any benefit

more but that&#39;s the

believe any of that nonsense about soaking exterior grade in miracle liqui= ds etc, its the voids that get you and the only ply with NO voids is marine= grade. (Atmospheric moisture gains entry into the voids and then it bubble= s up.) You can see this effect all over the country where 'experts' made an= d fitted shop signs with exterior grade ply.

Id be inclined to run a hardwood edging strip around the top edge at least = as moisture will first get in via the exposed edges of the ply. Rebated edg= ing strip should help keep this at bay.

[Grimly Curmudgeon]

Ah; differences - round here, you ask for shuttering ply you get structural and vice versa. It's waterproof though. There's only two grades here (ignoring marine, which is bloody twice the price), WBP and shuttering, which is just lower grade unfinished or badly finished WBP. A few years ago there was a bit of a cockup when somebody palmed off a load of interior ply onto a couple of stockists and much of it was used for exterior applications. What a mess that was, because nobody expected it, interior ply being almost unknown.

[Grimly Curmudgeon]

believe any of that nonsense about soaking exterior grade in miracle liquids etc, its the voids that get you and the only ply with NO voids is marine grade. (Atmospheric moisture gains entry into the voids and then it bubbles up.) You can see this effect all over the country where 'experts' made and fitted shop signs with exterior grade ply.

Decent quality WBP is plenty good enough - I have a sheet of ply on an workshop door that's remained unpainted for 13 years and no sign of delamination. I did seal the top edge with silicone, but that's all. However, during the boom , there was a lot of sub-standard shit dumped on the market with fake markings by unscrupulous operators out to make a quick buck.

[chris French]

In message , Grimly Curmudgeon writes

Yeah, I've got some WBP ply outisde here, totally untreated, and been about 5 years and it's fine.

Marine ply is a lot more expensive

[Andy Dingley]

Go to the best plywood specialist you can find (Avon Plywood in Keynsham is my favoured one). The extra range is worth the hassle, and it usually winds up cheaper too.

Plywood is expensive and comes in many grades. So a shop with a wide range sells you what you need, and no more. Buying better than you need gets _very_ expensive. Also "waterproof" plywood is generally a lie. The real waterproof grades cost serious money and aren't stocked outside specialists and boatyards.

I'd suggest a really good grade of spruce shuttering ply. This has replaced birch ply (the good furniture stuff, and a hellish price) for most things that I build. It's also far better than rainforest ply for not having voids etc. Needs good paint or varnish afterwards, but the cost / performance ratio is the best around.

[Andy Dingley]