Plywood Grading Rules :Part 15 Marine grade plywood
Marine plywood is manufactured from durable face and core veneers, with few defects; so it performs longer in both humid and wet conditions and resists delaminating and fungal attack. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. Each wood veneer will be the same species throughout (Fir, Okoume, and Meranti), and have minimal core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Water and Boil Proof (WBP) glue.
Okoumé and Meranti Marine plywood can be graded as being compliant with BS-1088 or BS-6566, which is a British Standard for marine plywood. Some marine plywood has a Lloyd’s of London stamp that certifies it to be BS 1088 or 6566 compliant.
BS-1088 grading requires the same species throughout (face, back, and core), defect-free A Grade Face veneer with no repairs. Back veneer is to have no more than two repairs. Both Face and Back Veneer are a minimum of 1mm thick after sanding and core gaps cannot exceed 1mm.
BS-6566 grading requires that Face veneers shall be at least 1mm thick after sanding. No wood repairs are used in the face. Inner ply’s can consist of two or more species of veneer and core gaps shall not exceed 3.2mm (1/8″). Gaps shall be putty filled to protect from moisture
Marine Fir AB is marine-grade plywood that is produced entirely of Fir veneers. The Panel is sanded on both faces. The maximum core-gap size permitted is 1/8 inch. Its exposure durability rating is EXTERIOR and the glue used is a water resistant structural adhesive. It is considered a premium grade panel for use in situations where these characteristics are required.
Marine plywood is frequently used in the construction of boats, docks, outdoor signs, counter top underlayment, and anywhere that requires prolonged exposure to outdoor elements.