How thick should plywood be for concrete forms?
Use 18 mm (3/4") for most slabs, walls and columns at ordinary 16" joist or stud spacing. Step up to 21 mm when joists open past about 400 mm (16"), a wall lift runs above 3 m, or the pump fills faster than roughly 1 m an hour. Keep 12 mm for light work and tight curves with close backing, and 15 mm for footings, low walls or sheets sitting inside a steel gang frame that already carries the load.
What size are formwork plywood sheets?
Sheet size and thickness are two separate lines on the order. North American forms and packs are drawn around 2440×1220 mm (8×4 ft), while European gang and table systems run on a 2500×1250 mm module. Our film-faced and MatteFace ranges come in both formats across 12, 15, 18 and 21 mm, so pick the format that drops into the frames you already own. 24 mm is not a stock forming thickness for us, so check before a takeoff assumes it.
Can you use 1/2 inch plywood for concrete forms?
Only for light work and tight curves, and only when backing sits close enough to keep the face from dishing. On a 16" joist grid for slabs or walls, 12 mm (about 1/2") deflects in the finish long before it breaks, so it is not a workhorse sheet at ordinary spacing. If the drawing still calls half-inch on a structural pour, tighten the joists or step the panel up before you pour.
Does thicker formwork plywood give more reuses?
No. Reuse follows the overlay, the glue class and how the crew strips and stores the sheet, so extra millimetres help with dents and flex but do not add cycles on their own. On our range, HDO Basic and Form Basic reach up to 10 reuses, MatteFace, Form Extra and Pro Form Lite up to 15, and Pro Form and HDO Premium up to 20. Eco Form Plus is rated up to 8 and Eco Form up to 6, whatever the caliper.
When should I step up to 21 mm formwork plywood?
Step up when the span, the head or the pour rate outruns what 18 mm can hold flat. On slabs that usually means about 500 mm (20") joist spacing or decks deeper than 200 mm (8"), and on walls it means lifts above 3 m or architectural faces where a 2 mm belly gets the panel rejected. Columns move to 21 mm once a face is wider than about 600 mm (24") or the yokes spread toward the top of a tall shaft, because the worst pressure sits at the base. A better overlay does not cancel that stiffness call.
What is the best type of plywood for formwork?
No single sheet is best for every pour, so match the thickness to the span first and then choose the overlay and bond class for the finish and reuse you need. North American jobs often spec HDO, or MatteFace for a matte cast face. Export and EU programmes usually run film-faced, with Form Extra on Superior Glue MUF (EN 636-2, not Class 3) and Pro Form or Pro Form Lite on phenolic Class 3. Put thickness, overlay, bond class, sheet size and emission class on the RFQ so we can match stock instead of guessing.
