Plywood data

I started a new thread because I think it is important to get to the bottom of this issue.

I googled marine plywood & within the same site there is conflicting info. No wonder this is myth based!

BTW, Why aren't we using this waterproof wood for our stringers??

From E-how site (Take with grain of salt):



Differences in the Marine Plywood Manufacturing Process

Waterproof wood is necessary for marine use since standard plywood grades rot after exposure to moisture.

In addition to Douglas fir, spruce and cedar, marine plywood suitable for boat and dock construction is made from long-leaf yellow pine, cypress, western larch, and eucalyptus.

The main difference in construction is that the surfaces of the plies are better smoothed so as to reduce the "voids," the micro-spaces in between layers, to tightly adhering joints that do not let destructive moisture in.

The adhesive is once again the water-resistant phenol-formaldehyde resin used in exterior-grade plywood.   All parameters of finishing, grinding and cutting are done with closer tolerances than standard plywood, accounting for the very high cost of marine plywood.

Different page, same site:

Marine plywood is a type of plywood made with waterproof adhesive


More data:

BS 1088 specification is a marine plywood specification that applies to plywood produced with untreated tropical hardwood veneers that have a set level of resistance to fungal attack. The plies are bonded with WBP glue.


WBP means “Water Boiled Proof”.We can say phenolic WBP glue,and we can say melamine WBP glue too.

WBP is only a kind of property/feature of glue. If a glue has WBP property, the glue will can be called WBP glue.

The difference of pheonlic glue and melamine glue.Phenolic glue is 50%~80% more expensive than melamine glue.

Melamine plywood can be in boiling water for 4~8 hours without delamination but phenolic plywood can be in boiling water for over 24 hours or even 72 hours without delamination.

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It is starting to look like 'buyer beware' is in order!

Thanks Alan! I will dig out the standard.

SNobsessed wrote: I was not able to access BS1088. So this is a dead end for me. I learned that not all marine plywood is equal. There are 2 types of glue - you want Phenolic. Species varies, so buyer beware. Still looking for the 'waterproof wood'!!!!

Chris here are the main points on BS1088 it will be good to see what you conclude and if my choice of wood matches yours "waterproof wood" two heads are always better than one

BS 1088 British Standard Specification for Marine Plywood manufactured from selected untreated Tropical Hardwoods

This is how several people have interpreted this standard and may differ to others, please make your own conclusion.

Specification.

This British Standard applies to plywood made with untreated tropical hardwood veneers having a suitable prescribed level of resistance to fungal attack with a bond of WBP glue quality between the plies. It does not need to be 'British made material'

Bonding WBP Glue line

Bonding meeting the test requirements of this British Standard and using an adhesive of the type which by systematic tests and by records in service of the product over many years has been proved highly resistant to weather, micro-organisms, cold and boiling water, steam and dry heat.
Species of Timber
If so specified by the purchaser, Gaboon or Okoume (Aucoumea klaineana), which is classed as non-durable, may be used provided that the name of the timber is included in the mark on the boards produced.

Quality of Veneers

Veneers may be rotary cut or sliced. The method of cutting is at the option of the manufacturer unless it is specified by the purchaser at the time of ordering. Veneers shall be smoothly cut.
Face Veneers
These shall present a solid surface, free from open defects. They shall be free from knots, other than sound pin knots, of which there shall be no more than 6 in any area 30cm square (1ft2), and not more than an average of 2 per 30cm square (1ft2) over the whole area of the board. The veneers shall be reasonably free from irregular grain, due note being taken to the characteristics of the species being used. Isolated pinholes not along the plane of the veneers, and occasional closed splits are permissible. Veneers showing compression failure shall be excluded. Occasional minor discoloration is permissible.
There shall be not more than one edge joint in any 30cm (1ft2) width of the board, and the veneers shall, when jointed, be matched for color. There shall be no end joints.

Core Veneers.

The requirements for core veneers shall be the same as those for face veneers, with the following exceptions. Small splits are permitted, and there is no limitation on the number of pin knots or edge joints. Discoloration is permissible, provided this is free from dote. Veneers need not be matched for color. There shall be no end joints.
Limits of Manufacturing Defects in Plywood
Defective Bonding Not Permitted
Pleats and overlaps Not Permitted
Gaps In faces. Not permitted. Occasional gaps that occur during manufacture may be repaired by means of well-fitted veneer inserts bonded with a complying adhesive. In Cores… In any edge of a board, not more than one gap, which shall be not wider than 0.5mm. Obviously the presence of defects in cores can only be judged by the appearance of the edges.
Moisture Content.
At the time of leaving the factory, finished boards shall have moisture content from 6 to 14%

Finishing.

Boards will be sanded on both sides equally
Length & Width
The length or width of a board produced as a standard size shall not be less than the specified size nor more than 6.3mm (0.25") greater than the specified size
Squareness
The lengths of the diagonals of a board shall not differ by more than 0.25% of the length of the diagonal

Thickness:

Tolerances vary as follows.
4mm +.02/-0.6 6mm +.04/-0.65 9mm +.06/-0.75 12mm +.09/-0.82
15mm +.1/-0.9 18mm +.12/-0.98 22mm +.16/-1.08 25mm +1.8/-1.16
From the above we can assume that 6mm material will arrive at thickness' between 6.04mm and 5.35mm.

Face Veneer thickness

For any three-ply construction, which applies to 3 and 4mm material, each face veneer shall be not thinner than 1/8" of the total thickness of veneers assembled dry.
Since the dry thicknesses of the boards are 3.6 and 4.6 respectively, we can assume that for these thicknesses only the face veneers will be as follows
3.6mm dry x 12.5% (1/8) = 0.45mm 4.6mm dry x 12.5% (1/8) = 0.575mm

Multi-Ply Construction.

This applies to boards thicker than 4.8mm (3/16")
Each face veneer shall be a minimum of 1.3mm and not thicker than 3.8mm. Each core veneer shall be no thicker than 4.8mm

This is the main parts the full BSI spec is £85.00