Grade of Plywood

[bob_tyler]

I wish to make some minor alterations internally on my Invicta. The area in question is well above the bilges and would be finished with paint or varnish.

Do I have to go to the extra expense of Marine Ply or would WBP grade be OK.

If the bilge water ever reached it I would consider that the boat had probably sunk.

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[DanTribe]

A very broad subject & open to loads of misinterpretations of course, but I believe that good quality birch WBP ply is far superior than cheap marine ply.
The cheaper marine plys are often described as "far eastern" The price is usually determined by the number of plys and quality of surface veneer, e.g. good 1 side or good 2 sides. Local timber merchants can be very helpful once you get them interested.
Dan

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[oldharry]

WBP can be used for interior fittings, but take great care to buy a good quality grade, and do not use it for anything structural. The core sheets are often softwoods, and will very quickly rot out if they do get damp or wet, so extra care needs to be taken to protect the end grains. Because of the inferior grade of timber used it is nothing like as strong, and unlike marine grade ply there may be quite large voids in the core laminates. Also even in a WBP grade ply the glues may not be particularly damp proof.

Do not even consider using non WBP grades of household ply. They will disintegrate in the damp atmosphere very quickly, however well protected and painted.

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[chippie]

If you go the WBP route, a couple of coats of thinned epoxy will help things.

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[stephenh]

In the trade, timber is classified as 'durable', 'very durable', 'non durable' etc.
I think that you will find that Birch is classified as 'non durable' and from this not a good idea.
'WBP' means 'water boil proof' and this refers to the adhesive used - not the timber. If you buy a WBP ply that does not have waterproof glue , then sue....
The test is that the glue should not give up after 1 hour of immersion in boiling water. The timber veneer might, but not the glue.
'Far Eastern' is what it says and will consist of veneers of varying quality hardwoods and there will be glue voids in the internal veneers.
BS 1088 - marine ply - consists of good quality hardwood veneers with no internal glue voids and is WBP. ( and from this rather expensive !!)
If you buy 'Far Eastern WBP' with a name like 'gaboon' for example, this will be the same timber all the way through. There will be some glue voids , noticeable only on the end grain, and the previous post saying "2 coats of epoxy" comes into play.
I would suggest 3 coats on all end grain - before you install.
Don't bother using Marine ply as such for interior work.

good luck

Stephen


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[bob26]

I've been round this track recently too Bob.

Alsford Timber in the South East sell marine ply BS1088 "not recommended for boatbuilding" which I think is a bit of a laugh. Even the catalogue admits its a contradiction in terms. The surafce veneer is very coarse and porous to my mind.

I have found cheaper boards marked "marine ply" but they vary tremendously - some seem half the weight of others and much softer. Travis Perkins hereabouts (Sussex) do one "far eastern" one that is very heavy and hard - but the surface veneers are not very pretty or consistent. Though its hard to tell how they will end up when varnished or oiled.

Structural strength was not crucial to my task - but whether marine ply or exterior grade I found it difficult fidning a cheap board that I was happy with the finish on to match existing veneers on the boat. I even considered veneering a cheaper board myself but was put off by the cost and unceratintly about how well I'd manage it.

You can buy interior ply veneered with all sorts of sexy woods but even for cabin furniture that seemed too risky to me.

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