How thick should plywood be for concrete forms?
18 mm (3/4") is the US default for slabs, walls, and most columns at ordinary joist or stud spacing. Step down to 12 mm only for light work and tight curves with close backing, and treat 15 mm as a residential footing or low-wall option when the gang already carries the load. Step up to 21 mm when the span opens, the pour gets tall, or the face has to stay dead flat between supports.
What thickness plywood for formwork?
Most US takeoffs land on 18 mm (3/4") because it matches common 16" joist and stud grids without surplus kilos on the hoist. 12 mm suits curved or light work with tight backing; 15 mm covers low walls and footings when steel already takes the load; 21 mm is the heavy option for wide spans, tall lifts, or fast pour rates. Thickness is a span call — overlay and glue class stay separate line items on the same RFQ.
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. Skip 12 mm (~1/2") on a 16" joist grid for slabs or walls — 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 overlay, glue class, and how the crew strips and stores the sheet; millimeters help with dents and flex fatigue, but they do not mint extra cycles on their own. Vinawood locked maxima stay face-led: HDO Basic up to 10, HDO Premium up to 20, MatteFace up to 15, Form Extra and Pro Form Lite up to 15, Pro Form up to 20, Eco Form Plus up to 8. A thicker Form Basic sheet is still capped by Form Basic chemistry, not by the caliper reading.
When should I step up to 21 mm formwork plywood?
Step up when the span, head, or rate outruns what 18 mm can hold flat. For slabs, that usually means about 500 mm (20") joist spacing or decks thicker than 200 mm (8"); for walls, lifts above 3 m or architectural faces where a 2 mm belly fails the pour; for columns, faces wider than 600 mm (24"). A pour faster than 1 m/hour or taller than 3 m is also a one-step bump — overlay grade does not cancel that stiffness call.
What is the best type of plywood for formwork?
There is no single best sheet — match thickness to span, then pick overlay and bond class for finish and reuse. North America often specs HDO or MatteFace for the 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 / Pro Form Lite on phenolic Class 3. Put thickness, overlay, bond class, size, and emission class on the mill RFQ so the mill can stock-match instead of guessing from a catalogue photo.
