Fruits Of My Labor (A-113)

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In the old days we had FinnPly and RussianPly
FinnPly birch was put together with Phenolic glue.

Russian aka BALTIC birch ply is glued with urea-formaldehyde (but who knows?) and would be considered INTERIOR grade plywood. It eventually will delaminate. 'Eventually' could be very short term in a damp environment.

FinnPly was also known as AIRCRAFT grade birch plywood -phenolic-formaldehyde - EXTERIOR grade. This grade is often stamped with the panel's ID, down in a corner or on the endgrain.
It is obviously going to be more expensive.
These are both imported panels. The best grade will have BS1088 stamped on it, especially the thinner millimeter panels that are used for wooden aircraft building.

You can't use the interior baltic stuff anywhere permanently on a boat. Even encapsulated with epoxy. Beware!


However,
the Ariel douglasfir bulkheads and tabbed-on plywood cleats that Pearson used for the chainplates was/is standard exterior fir ply. Settees and other furniture may have been a similar grade but I'm not sure. In my opinion the structural plywood in A-338 was whatever HomeDepot of the '60s had in stock. Believe douglasfir is rated moderately rot resistant. And the glue had to have been urea-formaldehyde. Still MUCH better stuff than baltic ply.
Except for obvious areas of rot (chainplates) the plywood has lasted pretty good for almost a half century!
(The difference imco is that fir has resin in the fiber, while birch has sugar in the fiber, which composts and black molds immediately.)