Ply wood delaminating

[pontoon flyer]

Hi to all
I bought some sheets of marineply 18mm the steets had stamps on confirming its marineply as well as the invoice. Cut up frame sections and varnish them and they have not split or delaminated, some off cut pieces were stored inside and I took them out wet them with water to see how to go about bending when I discovered they started splitting and delaminating at the ends before bending. Is this nornal, as I was under the impression marineply shouldn't delaminate because of the stronger glue compound used. Please advise

[PAR]

Your plywood should be stamped with a "BS 1088" or "WBP" (Water Boil Proof) adhesive, to be a true marine grade in your neck of the woods. If it's a "PowerPly" or "Eurolite" panel then it has a "MR-E1" stamp on it and is only a "Moisture Resistant" adhesive and not suitable for planking, but could be used as bulkheads or furniture inside the boat, if sealed properly.

It wouldn't be the first time, a manufacture mis-stamped a stack of panels, so check the lot numbers with the manufacture and see if they've had other issues. If it is indeed delaminating, then call the seller and demand a refund or replacement.

[alan white]

Good reason to do your own boil test no matter where you got the ply. What is advantagious about boil tests, in addition to peace of mind, is that plywood having no labelling, presumed to be interior grade plywood, can turn out to be boil-proof.
such was the case with thirty sheets a friend and I purchased together years ago from a discount salvaged goods store. The sheets were 1/4" 7 ply birch. They passed the boil test on a piece of the first sheet, and so we bought the rest--- at $10 each.

Alan

[zigzag]

I have experienced problems in asia buying BS standard or even exterior glue 3mm luan ply. Cylinder moulding technique is appropriate for fast building but without confirmation of the glue type perhaps folly. How long for the boil test to confirm application of the plywood? I don't hang around the kitchen a lot so what would be the minimum time?

[alan white]

A half hour after it begins boiling is enough. Then let it sit in water overnight if it shows no delamination and check again. These things are dependant on the size of the piece---- a few pieces 3" x 3" together makes more sense to me than one big piece. If the glue holds in all pieces, you have good ply.