Marine Plywood is manufactured from a selection of hardwood species. The board is normally manufactured with an odd number of plies, each ply being oriented at 90 degrees to the one bonded to it, to create a balanced construction. The face and reverse veneers are almost always oriented in the direction of the longest dimension. Marine Grade plywood differs from most other hardwood plywood’s in 4 specific ways:

1. The hardwood species are from a select group, known to be naturally resistant to fungal decay and beetle larvae infestation. BS 1088 describes “Standard Marine Plywood” as “made throughout of timbers having a durability of Class 3, BS EN 350-2 or better” with a minimum nominal density >500 kg/m3. BS 1088 also allows for a “Lightweight Marine Plywood” of durability Class 4, BS EN 350-2, or better and of density <500 kg/m3. In either case, up to 5% sapwood is permitted in any veneer.
2. The quality of the core veneers is generally the same as the face, regarding the absence of open defects, resulting in a virtually solid panel with few core voids. This is a guide only and BS 1088 is specific regarding the actual type, size and frequency of the defects permitted in outer and inner plies.
3. The standard specifies minimum thickness of veneer: outer plies minimum 1mm after sanding; inner plies maximum of 4.8mm for panels more than 3.8mm nominal thickness. In practice, inner plies are generally thinner. This gives rise to a greater number of thinner veneers than many other plywoods. More veneers require more glue lines, thus increasing the glue content of the panel giving rise to greater stability. In panels of 6.5mm or less, a minimum of 3 plies is required.
4. The proportion of veneer oriented with the grain parallel to the face must be between 40% and 65% of the nominal, unsanded thickness of the panel.