The evils of plywood...

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pauls_SPT

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I'm not sure if I'm allowed to say "plywood" here /forums/images/graemlins/smile.gif

I'm going to replace the rotten knees which hold my deck-beams in place on my boat and I'm going to use some of the 18mm ply I've got stacked about the place. Although using ply may not seem to be quite in the spirit of restoring a classic wooden boat, in my defence, it seems to be what was used before. However, if there's one thing ply loves doing, it's delaminating and turning into a ripply piece of modern art, so...how best to avoid that? Is there some wood preservative that I can paint on that anybody would recommend? There seem to be plenty of wood treatments available (ronseal et al), but I can't find anything specifically good for plywood...

Any help, thoughts, sucking in of breath through teeth etc will be much appreciated /forums/images/graemlins/smile.gif

Thanks,

Paul
 
I uses some ply pieces on my old boat for this job.

Once you cut them to size, trial fit them, and drill all the holes you need for the fastenings. Then coat the whole thing in epoxy, making sure you really saturate the end grains.

Then fit and paint. Or paint then fit depend on how you want to do it. The epoxy will completely waterproof the ply, and therefore, it should last a very long time. Use a good quailty ply though. See my thread below where we were discussing ply a bit - my boat is partly constructed from the stuff.
 
First, what alb40 says is fine.

Second, my boat is mostly ply so no worries about that, prior to the advent of eopxy it has a life of about 15 years if looked after, with epoxy its a lot more.

Third, the istory of ply can be traced back to a launch called Consuta built I think by Saunders Roe in about 1890, Consuta is Latin for sewn together, she was built of veneers interleaved with calico and linseed oil sewn with copper wire, for me that's good enough provenance. she is sometimes used as Umpire's launch for the Boat Race.
 
Thanks for that /forums/images/graemlins/smile.gif

I wondered how old Ply was - my boat's 1930's vintage and I was surprised to find ply as part of what was clearly original construction...

Time to break out the West epoxy, then...

Thanks,

Paul
 
..oh hang on a moment...

I dont think ply was being made in flat sheets until sometime later, only that the notion of using veneers in layers was used that early.

I think flat sheets started in the 40's.
 
All as above but do remember to make sure that the old ply you are gluing to is completely dry. I am doing some patching on the cabin side at the moment with tube heater to provide some background warmth. A router set to 9 mm was effective for making a lap joint in the 18 mm ply.

delaminating.jpg


The small hole is where I cut with a hole saw to see if it the ply was dry lower down.

cut_out.jpg


I routered the lap before cutting out to give more support for the router.

prepared.jpg


Photo of finished article to follow!
 
[ QUOTE ]
I'm not sure if I'm allowed to say "plywood" here /forums/images/graemlins/smile.gif

I'm going to use some of the 18mm ply I've got stacked about the place. Although using ply may not seem to be quite in the spirit of restoring a classic wooden boat, in my defence, it seems to be what was used before. However, if there's one thing ply loves doing, it's delaminating and turning into a ripply piece of modern art, so...

[/ QUOTE ]

<<18mm ply stacked about the place>> Depends what it is as to whethr its suitable. If its proper marine stuff - not just BS1088 which can be rubbish - it will be as good as laminated timber. 'Proper' marine ply will be the same hardwood in all laminations, which will all be the same thickness.

Look at the edge of the board: if the internal laminates are whitewood, and thicker than the surface veneers, then it is not suitable for structural work. The internal veneers will be softwood, which will rot out if it gets damp, they will not be anything like as strong as hardwood, and there may well be quite large voids where the laminates join internally, making for serious weakening of the board at that point.

Fine for furniture and other internal non structural items, but forget it for structural work.

As for 'ripply art work' - only happens if you use the kind of ply I describe above.

Ply has its place in Classic boats - some pre-war boats used ply, and the technology advanced rapidly during the war as a quick, cheap means of producing boats, and other wooden structures.

There are any number of plywood boats around dating back to the 60s and earlier. They survived because builders had the foresight to sheath them and protect the plywood. Those that were not sheathed and protected are no longer with us, or are too far gone to be worth rebuilding.

Painted marine ply has a practical life span of around 25 years. If it is encapsulated by sheathing, or soaking in epoxy, it will still be as good as new. My 60s Eventide is, as are many of her sisters.
 
For the sake of completeing the set, here it is glued in place. All joints were primed with neat warmish epoxy with the ply well warmed first. I used epoxy with microfibres as the glue. If I had to do it again, the vertical joint would have been a half lap joint as well.

glueing.jpg
 
Thanks for all of that /forums/images/graemlins/smile.gif

The pictures are very interesting - I've been musing on the various ways I could fit my cab-sides to my superstructure...

My 18mm play is, indeed, marine standard although, to be honset, I can't see any difference between it and WBP(?) ply I can get from builders merchants...I guess it must be down to the glue and the internal structure, like you say...

My next question, then; my boat appears to have been made from whatever was lying about the place in the boatyard with regards timber sizes (such eclectic sections as 5/8 x 1,7/16) Ask for that sort of section in a woodyard and they give you "that look", so I'm going to have to go for the closest I can get and then cut it down.

I'm planning on using Pressure Treated timber to give my boat a fighting chance at lasting a few more years, but the problem comes from when I start slicing it up. The woodyard says just to bundle all my cut lengths up, bring them back and they'll pressure treat them again, but this would be very awkward, as I'd have to practically build my boat, then take it all apart before building it again.

How about if I used untreated timber and then just painted the whole thing with cuprinol (or similar)? Given the choice between the two options, does one of them stand out as the "obvious" way of doing it, but I just can't see it?

Again, any thoughts, opinions or stroking-of-beards is much sought after /forums/images/graemlins/smile.gif

Thanks,

Paul
 
Which bits of wood were you thinking of pressure treating? If you are gluing with epoxy I would think that clean, dry and otherwise unadulterated wood is what you need. If you are patching ply and coat with epoxy then, in theory, the ply will stay dry and therefore rot is not an issue. In theory!
Having just been given Pardey's book "Details of Classic Boat Construction" I discover that not everybody thinks that the sun shines out of a bottle of epoxy resin. Not that anybody who has used any amount of it would anyway. But perhaps that is a question for a new thread.
 
This is all the beams and supports for my decks, although not the decks themselves...

I have to admit, I was hoping to avoid epoxy as much as I could, but it seems that it's THE standard way of protecting and sticking together pretty much all wood...

Paul
 
It is certainly the best stuff to use for sticking bits of wood together and protecting them.

If its done nicely, and painted well, who will every know you've used it? (unless you tell them?) /forums/images/graemlins/grin.gif
 
If the faying surfaces are fair and true - ie you don't need to gap fill at all, there are other easier to use glues. I have never used it but Extraphen (I think it is called) seems to be a favourite of some. I have used Balcotan for laminating and similar jobs. It needs very close clamping and it does not gap fill at all if you want to maintain the strength But is relatively quick and easy to use. I am not sure what it is "approved" for, but used it to laminate a new iroko stem for an old clinker dinghy which lives on a swinging mooring. Been on a couple of seasons so far...
 
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