Birch ply stability

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KAM

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I have bought a sheet of 10mm wbp Birch ply to refurbish the inside of some internal lockers. I went for multiply Birch as it's nicer to work with than cheap hardwood ply. Unfortunately it's proving to be very unstable compared with hardwood and is starting to warp quite badly. I can correct most of it as I am working but worried about stability once its on the boat. I've previously used cheap moisture resistant hardwood ply which has lasted a long time without any problems. Anybody out there had any experience with Birch ply on a boat.
 
All of the veneered and painted plywood on our Finngulf 33 was birch as far as I know. We once panelled the ceiling of a sports hall with timber and birch ply was selected for its stability, again no problems; the floor of my Estonian made trailer which has sat outside in the rain now for 16 years is a single full sheet of 12mm birch ply and it is still intact and flat. I did turn it over and put a coat of 2 pack epoxy on the new top side a couple of years ago, still no sign of warping, very flat indeed despite only coating one side.
I am an enthusiast for good quality Finnish birch ply and I am surprised you had problems
 
I've used exterior grade Birch extensively and never had a piece warp or move. As an example we had the poly wash boards of our yacht broken in a break in. As a temporary measure we used a piece of offcut birch ply that was to hand. It served in that job in all weathers for many years and is still kept as spare / replacement. As an aside I came across Birch ply while doing some work for a very large motorhome / caravan manufacturer. I found that the floors of these units are decked in Exterior grade Birch. This is the surface that suffers all the road dirt and rain wash while on the move. It was the plys longevity in this situation that convinced me to use it a lot. Since then I've never known a piece rot or warp and it is excellent to work with, far better than cheap marine plys that splinter etc! Our current craft is 14mtr and fitted out through out with birch ply that has never given a problem. I can only think are you sure its exterior grade Birch?
 
Quandary said:
All of the veneered and painted plywood on our Finngulf 33 was birch as far as I know. We once panelled the ceiling of a sports hall with timber and birch ply was selected for its stability, again no problems; the floor of my Estonian made trailer which has sat outside in the rain now for 16 years is a single full sheet of 12mm birch ply and it is still intact and flat. I did turn it over and put a coat of 2 pack epoxy on the new top side a couple of years ago, still no sign of warping, very flat indeed despite only coating one side.
I am an enthusiast for good quality Finnish birch ply and I am surprised you had problems
Click to expand...

+1
 
I have had pieces of good quality baltic birch at the bottom of a barrel of water for over a year with no separation of the veneers
told the people i bought it off and they were surprised as well
the baltic birch i have used is void free and dense only down side have noticed its prone to dote or datk mold stains if left for too long

If your ply is cupping warping there are probably other factors at work
qualiity of material /movement /stress/uneven moisture zones

Some are using this material as deck substrates after expoy coating
 
Great thanks very much for the helpful replies. That gives me a lot of confidence. The jobs coming together nicely now fortunately the shelves and bulkheads are pulling it all into shape. I've also left a sample out in the rain to test.
 
There's a number of website that list timbers and their durability. Birch in them is generally listed as poor durability. I know that it was stability that was questioned originally, but doesn't stability include durability as well as dimensional stability?
I know that when I cut birch (European Birch) for firewood it doesn't last 2 seasons, and I have to be sure to use it up. If it gets wet, it starts to rot in months - that seems to support the durability 5 rating given by (for example) TRADA ( https://www.trada.co.uk/wood-species/birch-european/) the lowest rating.
I'm no expert in this, but wonder about the discrepancy between what's said about it, and the published info.
Or, are we talking about a different timber?
My understanding of WBP is that this relates to the glue used, not the timber - but both must be important?
What did I misunderstand here?
 
I burn quite a lot of birch and under cover even the branches seem to keep for 5 years or so, unlike lime which is soft in a year. The last tree that I took down, birch, about 60cm dia. at base, and 20m. high had trunk timber that feels as hard and as heavy as oak, while the branches which I am burning now are lighter softer and reasonably easy to split.
The durability may be a factor of where it is grown like it is for larch. Siberian larch, slow grown in a short summers is visibly denser than even the best Scottish hybrid larch.
 
Thanks chaps;. You've changed my mind about birch. I'd always unde4stood birch to lack durability - good indoors but a no no outside. And yet I'd used 1/8 inch birch aeroply....wonderful stuff and presumably good for aircraft without dissolving in a shower or a cloud but never really got the hang of the paradox.
 
MM5AHO said:
There's a number of website that list timbers and their durability. Birch in them is generally listed as poor durability. I know that it was stability that was questioned originally, but doesn't stability include durability as well as dimensional stability?
I know that when I cut birch (European Birch) for firewood it doesn't last 2 seasons, and I have to be sure to use it up. If it gets wet, it starts to rot in months - that seems to support the durability 5 rating given by (for example) TRADA ( https://www.trada.co.uk/wood-species/birch-european/) the lowest rating.
I'm no expert in this, but wonder about the discrepancy between what's said about it, and the published info.
Or, are we talking about a different timber?
My understanding of WBP is that this relates to the glue used, not the timber - but both must be important?
What did I misunderstand here?
Click to expand...

It is a strange situation and if memory serves me right the BS1088 standard for 'marine ' ply had no requirement for any kind of durability level of the wood used in its construction.
just had a quick look and this page from Southern Timber discusses birch ply and mentions how quality can change dependant upon source....https://www.southern-timber.co.uk/product/interiors/hardwood-ply/birch-ply/
Maybe need to ensure its Finnish or similar in future!
 
Just finishing the job so thanks for the info. Interesting discussion on durability. I was going to say there not many Mosquito aircraft left but was surprised to see there are still 30 with 3 flyable so durability must be reasonable. On the subject of durability the lockers i am replacing are on a quality boat built 40 years ago. I was surprised to find that the lockers were built from 10mm melamine faced chipboard. They were in reasonable condition but I just noticed this season a small amount of rot caused by an undetected deck leak which must have been there at least 10 years. I am very surprised the chipboard lasted that long. I wondered if it was some special material they were using back in the 1970s.
 
I don't know about the '70s, but in the 90's you could get water resistant chipboard. I knew someone who was refitting a canal boat with it and he seemed quite confident that it would last. No idea if it did, as I lost touch soon after.
 
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