Plywood is a composite wood made of layers of wood, thin sheets that are laid together and glued. These thin sheets of wood, which are in both interior and exterior plywood, are called veneers.
The grain in plywood, both in interior and exterior plywood, is alternated for strength, though the grain runs in the same direction on both outside faces of exterior and interior plywood. The plywood is bonded under heat and pressure.
Glues in Exterior Plywood
Exterior plywood is also called outdoor and marine-grade plywood. Exterior plywood is created with water-resistant glues, which also help the exterior plywood resist rotting. These glues are phenol-formaldehyde based. They also help the exterior plywood keep its strength in high humidity conditions.
Adhesives which are used in exterior plywood have been a subject of environmental questions since the formaldehyde will release into the atmosphere over time.
High-strength exterior plywood, a special grade of exterior plywood known as aircraft plywood, made from hardwoods such as mahogany, was used in the manufacturing of World War II fighter aircraft.