Why does plywood vary so much in price?
Two sheets of the same thickness can differ in price several times over. What is actually different inside them, what shuttering ply really is, and when the cheap sheet is the right buy.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 4 min
Short answer
Price tracks the species, the number and quality of the plies, the glue and the face veneer. A cheap sheet has fewer, thicker core plies with voids and overlaps, a paper-thin face and an interior glue. Birch ply has many thin plies, no voids and a face thick enough to sand. Look at the cut edge in the rack — it tells you which one you are holding.
"18mm plywood" describes a category, not a product. The range in a single merchant can run from a cheap far-eastern hardwood ply to Baltic birch at several times the price, and the difference is entirely inside the sheet where you cannot see it from the face. Fortunately the edge is visible, and it tells you almost everything.
Step by step
- Count the plies at the cut edge.More plies for the same thickness means thinner veneers, more glue lines, more stability and more strength. An 18mm birch sheet may have thirteen plies; a cheap 18mm sheet may have five thick ones. This is the quickest quality test there is.
- Look for voids and overlaps in the core.Run a fingernail along the core layers at the edge. Gaps where core strips did not meet are voids, and they are why a screw near an edge pulls out and why a routed edge looks like honeycomb. Overlaps, where two strips doubled up, telegraph through the face as a ridge under paint.
- Judge the face veneer thickness.A face you can sand is a face you can use. A paper-thin face sands through to the ply below at the first pass and cannot be planed at all. Look at the very outer layer at the edge and compare sheets.
- Check the bond class separately from everything else.The glue decides how the sheet behaves when wet, and it is a completely separate specification from the face grade. Exterior and marine grades use a weather- and boil-proof adhesive; interior grades do not. A beautiful birch sheet with an interior bond still delaminates outdoors.
- Understand what shuttering ply is.Cheap structural plywood made for concrete formwork, often with a rough face and sometimes phenolic-coated. It is cheap, strong enough for its job, frequently full of voids and patches, and is entirely reasonable for hidden structural use, temporary work, jigs and shed floors. It is a poor choice for anything visible or edged.
- Know what you are paying for with birch.Baltic and Russian-standard birch ply is dense, void-free, made of many thin plies of a single species and has a face good enough to varnish. That is why furniture makers use it and why it costs several times a builders ply. It is also heavy and hard on blades.
- Buy down deliberately, not accidentally.Cheap ply is genuinely the right buy for a shed floor, a workshop bench top, formwork, hidden framing and anything that gets covered. It is the wrong buy for anything with a visible edge, anything screwed near an edge, and anything that has to stay flat and precise.
- Check the sheet is flat before you buy it.Cheap ply is more likely to arrive bowed or twisted and less likely to flatten out. Sight along the sheet in the rack; a sheet that is already curved will not improve.
Tips
- Ask to see the back of a sheet in the rack. Face grades are lettered and the two faces are graded separately, so a sheet sold as a good grade may have a much lower grade on the reverse.
- Patched faces — where a knot has been cut out and a boat-shaped plug glued in — are normal on many grades. They are fine under paint and obvious under varnish.
- For visible work where birch is too expensive, hardwood-faced ply with a birch or poplar core is a good middle ground: an acceptable face at a fraction of the price, on a core good enough to edge.
Common mistakes
- Buying by thickness and price alone — The two 18mm sheets at either end of a merchant's range have almost nothing in common. Thickness tells you what fits; it says nothing about strength, screw holding, flatness or edge quality.
- Using cheap ply where a screw goes near an edge — A void under the screw means it has nothing to grip. Edge fixings need a void-free core, which in practice means paying for a better sheet.
- Assuming exterior grade means good quality — Bond class and construction quality are independent. A weather- and boil-proof sheet can still be full of voids with a paper face. Check both.
Questions people ask
Is marine plywood worth it?
Only where it earns it. Marine ply is a high-grade, void-free, durable-species sheet with a weather- and boil-proof bond, made for boat building, and it is expensive. For a bath panel, a shed floor or a garden project, ordinary exterior-grade plywood is almost always the sensible choice and marine ply is overspecified.
What does WBP mean?
Weather and boil proof — an older British description of an adhesive that survives weather exposure and boiling water. It describes the glue only, not the timber or the construction quality, and modern boards are more usefully described by their bond class and standard.
Why is birch ply so heavy?
Birch is a dense hardwood and the sheet is void-free, so there is simply more wood in it than in a lighter softwood ply of the same size. That density is exactly what gives it the screw holding and the edge quality people buy it for.