What is plywood made of?
Plywood is made of thin wood veneers (called plies) bonded with a thermosetting adhesive. The veneer can be hardwood (Acacia, Eucalyptus, Hevea, Birch) or softwood (Douglas fir, Southern pine). The adhesive can be urea-formaldehyde for interior use, melamine-urea-formaldehyde (MUF) for humid conditions, or phenol-formaldehyde for full exterior exposure. Each glue chemistry sets the panel's moisture envelope.
How is plywood made step by step?
Plywood manufacturing follows an eight-step process: (1) log selection and debarking, (2) conditioning in hot-water vats, (3) rotary peeling on a lathe into a continuous veneer ribbon, (4) clipping and sorting by grade, (5) drying to 6 to 10% moisture, (6) glue spreading and layup with grains cross-banded at 90 degrees, (7) cold press followed by hot press at 120 to 150 degrees Celsius, (8) trim, sand, and grade. The full cycle takes 4 to 8 hours of factory time.
What is the difference between plywood and OSB?
Plywood keeps the wood as continuous veneer through every layer; OSB chips the wood into 100 mm strands and bonds them with phenolic resin. Plywood holds screws better across the panel thickness and resists edge swelling. OSB is cheaper at the same thickness and matches plywood for in-plane sheathing strength when dry, but swells permanently at edges when wetted.
Is plywood waterproof?
Plywood is not waterproof in absolute terms, but the bond class determines how much moisture it tolerates. Urea-formaldehyde plywood (EN 314 Class 1) is interior only. MUF-bonded plywood (Class 2 / EN 636-2) handles humid climates and short-term wetting. Phenolic-bonded WBP plywood (Class 3 / EN 636-3) survives boiling water and sustained outdoor exposure. Marine plywood is the highest exterior grade with phenolic glue throughout and a denser hardwood core.
What standards govern plywood quality?
Plywood standards vary by export market. In Europe, EN 13986 governs construction-grade plywood and CE marking, with EN 314 and EN 636 covering bond quality and service class. In the US, PS 1-19 covers structural plywood and PS 2-18 covers wood structural panels, both administered by the APA. India uses IS:303 for general plywood and IS:710 for marine. Korea uses KS F 3101. The UK uses UKCA plus BS EN 13986 post-Brexit.
Why is plywood made with cross-grain layers?
The cross-grain layup is what makes plywood structurally useful. Wood is strong along the grain and weak across it. By rotating each ply 90 degrees relative to its neighbours, the composite panel is strong in both directions, resists warping and splitting, and holds screws without splitting the way a solid board would. The odd number of plies (3, 5, 7, 9, 11, 13) keeps the panel balanced about its centreline so it stays flat under humidity changes.
How many plies are in 18 mm plywood?
Eighteen-millimetre plywood typically has 11 to 13 plies of 1.5 mm veneer in premium grades, with calibrated formwork plywood at the upper end. Lower grades may use 9 plies of thicker veneer, which is acceptable for general construction but holds screws less well and shows more void area at the edges.
