Plywood for exterior use FAQ

Either marine ply or exterior ply is what you want for use outside. More expensive than ordinary ply, though.

We used Jabroc in the aircraft industry.

Wasn't it called 'Weyroc' - used in propellers?

It seems, that was a chipboard product according to the Weyroc blurb. Jabroc was a type of marine ply, with a wide range of thickness. We used it for support stands and bases. Not sure if it was used in the construction of the Mosquito.

I don't know if the grades have changed but yes, you are right to ask:

MR (moisture resistant) is not suitable for outside work.

WBP (weather and boil proof) was the only standard for the unofficial 'exterior grade' but was a standard which applied only to the adhesives used in the manufacture and not to the quality of veneer. Hence the cheapest shuttering ply was WBP as well as very good quality boat building ply, despite the two products being very different. Really you need a supplier who knows what they are talking about to get a good product without voids and with good veneers without overlaps.

Marine ply strictly refers to very superior and expensive Lloyds approved boat building ply and you don't need it for a gate.

TW

Helpful to know.

I'll investigate that.

Oh good, that's the £85 stuff.

Thanks

Adrian

Look for WBP (Water and Boil Proof) - that will not delaminate in the wet, or when heated in the sun when damp etc. Don't bother with Marine ply as it is significantly more expensive and its main extra feature (no internal voids) is not going to matter for this application.

OSB3 is also ok for use outside and might be cheaper (and a bit uglier)

Shuttering ply is also normally WPB, but made from spiral cut laminations, so does not look as nice, but is cheaper.

For your structure, a framed ledge and brace is a good option for a strong gate:

In message <v7ruen$1tkuv$ snipped-for-privacy@dont-email.me, John Rumm snipped-for-privacy@nowhere.null writes

Thanks for that. The gates would be painted, so the appearance of the ply probably wouldn't be an issue.

Ooh, very helpful.

My starting point is the existing gate design which has one brace rather than two, but with one rail at the top (as per the wiki), and a second one slightly lower down (~100mm). That works with the location of the hinges (heavy duty gate hinges rather than "door" hinges"), which might be awkward to relocate (due to the location of their mounting on the gate posts, but I'll have another look). The existing gates also have a timber cap which is ~10mm wider than the gate on each side ensuring that the rain drips off it, rather than running into the top of the frame.

Current timbers are 70x45 apart from the top rail which is 62x45. I think it would be simpler to use the same size timber all round.

Adrian

That is not uncommon. One technique takes one long brace top to bottom, doing a half lap over the middle rail if their is one.

Yup, top cap is very will worth having - it keeps the bulk of the water out of the end grain at the top of the gate.

They often use a thinner timber on the middle and bottom rails, so that the cladding can just pass over them, rather than needing to stop and be rebated into the edges.

I once used what was sold as marine ply for the gable end of a concrete garage. It took about 2 years before it started delaminating, even though the exposed edges had been varnished, & 5 years before it had to be replaced with vertical T & G.

Unless you're prepared to pay a lot of money, or can tolerate shuttering ply or OSB, I would forget the skin and use treated softwood. Perhaps vertical T&G, or gapped if that's your preference. It would look nicer and avoids the risk of plywood delamination. If, in the future, something rots then all you have to do is cut-out the affected piece and scarf in a new one.

Edited to add: I've just seen JR's reply, suggesting something similar.

In message <v7sc63$23pj7$ snipped-for-privacy@dont-email.me, John Rumm snipped-for-privacy@nowhere.null writes

Overnight/this morning, I've been thinking (often dangerous). I was looking at ply for the skin as that is what is being used at the moment, and my previous (limited) experience of using tongue and groove outdoors was that it warped badly, but I'm starting to wonder if it might be a better move than ply, apart from anything else, I can get lengths of it in the car, which I can't with ply (no trailer or roof rack), so I would have to get the ply delivered. A simple top to bottom skin of T&G might be a suitable alternative, rather than rebating it in (as on the Wiki page). If so, which T&G to use ? A quick look online suggests shiplap laid horizontally could be the best solution.

Adrian

I would recommend T&G vertical cladding often called vee boards because the tongue and groove have an angled edge which when pushed together produces a v shape. The pictures below show my garage side door and the close up shows the effect of the v-shape

Front

Richard

In message <v7tn1n$2am6d$ snipped-for-privacy@dont-email.me, Tricky Dicky snipped-for-privacy@sky.com writes

Thanks for those. Looks good.

Avoid sheds was top of the list. It isn't just the treatment, getting stuff that is straight is a challenge. A few years back, I wanted some

Adrian

Nice job!

You can also get a T&G called Bead and Butt, which on the tongue side has a bevel, then a bull nose. So when it goes together you get an attractive bead profile at each board joint.

The back of this shelf was made form some boards left over from my bathroom build:

The T & G that I got from a local builders merchant, who have their own timber yard, was treated (tanalised ?), has a rounded face, flat back & is somewhat thicker than the flimsy stuff sold in 'sheds'.

In message snipped-for-privacy@ffoil.org.uk>, Adrian snipped-for-privacy@ku.gro.lioff> writes

I've been doing some more digging on this (a sort of measure twice cut once approach). As the gates are outside, but not touching the ground, I think I need timber that is treated as Class 3. On that basis, I've been looking at the websites of the local suppliers, and it seems that they all do it, and at the right sort of sizes, but it is all rough sawn, rather than planed. As I doubt that I could convert rough sawn into consistently sized planed, that means that I'm stalled. Do I need Class 3 ?, if so, what is a sensible way to proceed ?

Adrian

If you are going to paint the timber, then think of other outside things that you paint; what sort of timber do they use. On the other hand, if it's going to be stained with fence paint, then you don't need planed timber. I have a pair of gates which are made that way. They've been up for at least

In message snipped-for-privacy@candehope.me.uk>, charles snipped-for-privacy@candehope.me.uk> writes

My intention is to paint. I don't know what the other outside timber is, as it has probably been in place since the late 30s (house facias) or late 40s (garage facias, doors and windows).

Adrian