Atmospheric Corrosion
149
4.8.5.1 Plywood
Wood layers or plies of veneer, or veneer and lumber in which alternate
plies are laid with the grain at right angles, are given the name plywood. By
alternating the grain direction of each ply, in adjacent plies, the two face
directions are equalized in strength, stiffness, and dimensional changes.
Plywood is produced as either interior or exterior type. Exterior-type plywood is designed to retain its shape and strength when repeatedly wetted
and dried under adverse conditions and be suitable for permanent outdoor
exposure. It is sometimes referred to as marine plywood. Exterior plywood is
usually bonded with hot-pressed phenol resins.
TabLE 4.23
Resistance of Wood to Decay
Softwoods
Hardwoods
Bald cypress
Ε
Ash
Ρ
Douglas fir
F–G
Aspen
VP
Hemlock, western
Ρ
Balsa
Ρ
Larch, western
F
Beech, American
Ρ
Pine, ponderosa
F
Birch, yellow
G
Redwood, virgin
Ε
Cherry, black
Ε
Spruce, Sitka
F
Chestnut, American
Ε
White cedar
Ε
Cottonwood, eastern
VP
Elm, American
F
Elm, rock
F
Hickory, shayback
G
Magnolia, southern
P
Mahogany
G
Maple, sugar
Ρ
Maple, silver
Ρ
Oak, red
G
Oak, white
G
Sycamore
Ρ
Sweetgum
F
Walnut, black
Ε
Poplar, yellow
P
Note: Ε = excellent; G = good; F = fair; P = poor; and VP = very
poor.
Source: From Reference 23.