Marine Plywood Grades

BS 1088

• Although a British Standard, it is used by marine plywood manufacturers world wide. The plywood does not have to be of British Manufacture. It is an extensive document which details all characteristics of the plywood.
• The BS 1088 standard is a marine plywood specification that applies to plywood made from untreated tropical hardwood veneers that have a stated level of resistance to fungus growth.
• BS 1088 plywood must use a glue, which has been tested and shown to be highly resistant to weather, micro-organisms, cold and boiling water, steam and dry heat. There are standard BS tests for the glue.
• The Face Veneers must have a solid surface without open defects. Face veneers must be free of knots except "sound pin" knots, (no more than six in any one square foot,) the average of pin knots cannot exceed 2 per square foot over the whole surface of the plywood sheet. The grain in the veneers should be reasonably regular. Edge joints are limited, and end joints are not permitted.
• Core veneers requirements are similar to face veneers except that slits are allowed as long as they are small. Pin knots and edge joints are also allowed. As in face veneer, end joints are forbidden.
• Manufacturing Defects are strictly controlled. Poor bonds, overlaps and pleats, and gaps in faces are not allowed. Gaps may be filled using veneer inserts glued with appropriate adhesive.
• The Moisture content of the plywood must fall between 6% and 14% when it leaves the factory.
• Boards will be equally sanded on both sides.
• Finished size The length or width of a standard sized sheet can not be less than the stated size nor more than 6.3 mm (0.25") larger.
• Squareness -- The lengths of the diagonals of a sheet shall not vary by more than 0.25% of the length of the diagonal.
• Thickness tolerances:

4 mm +.02/-0.6 ; 6 mm +.04/-0.65 ; 9 mm +.06/-0.75 ; 12 mm +.09/-0.82 15 mm +.1/-0.9 ; 18 mm +.12/-0.98 ; 22 mm +.16/-1.08 ; 25 mm +1.8/-1.16

• Face Veneer thickness -- For any three-ply construction, each veneer sheet will not be any thinner than 1/8 of the total thickness of veneers assembled dry. Multi-Ply Construction-- This applies to boards thicker than 4.8 mm (3/16")

Each face veneer shall be a minimum of 1.3 mm and not thicker than 3.8 mm. Each core veneer shall be no thicker than 4.8 mm

BS 6566

This standard is very similar to the BS 1088 with somewhat reduced quality.

It is a marine plywood standard using the same glues, but has somewhat more relaxed requirements as to the quality of the veneers. The face veneers are often of slightly lower grade and thinner. There are no voids and requirements for joins are similar.

It is generally considered an excellent material if not as pretty as the higher grade. Bright finishes are not necessarily as successful as with the BS 1088. I have used both grades and have not seen any defects in either.

Exterior Plywood

There are many exterior grades being manufactured. The glues are usually essentially the same as the marine grades. The outside veneers vary a great deal depending on the chosen grade. There is a possibility of voids. Boats have been successfully built using higher grade exterior plywood.

AS/NZS 2272

This is an Australia / New Zealand standard. Marine Plywood manufactured to AS/NZS 2272 standard, is a structural plywood intended for hulls of boats and other marine applications. It has a Type A (wbp) phenolic bond glue and is manufactured from woods based on density, bending strength, impact resistance and surface finishing characteristics.