ForMatter/Processes/formative/Concrete Casting (Formwork)
proc_concrete_casting

Concrete Casting (Formwork)

formative · concrete pouring, concrete molding, cast-in-place concrete, precast concrete, GFRC casting, concrete formwork
highlast updated 2026-04-28

Pouring wet concrete into a mold — wood, plywood, steel, fabric, foam, sometimes 3D-printed plastic — and letting it harden into the shape the mold described. The mold is the form. Everything else about the surface, the joinery, the texture, follows from how the formwork was built. The cast is true to the form because nothing about the concrete resists; the concrete is liquid until it isn't, and what was a soft pour is a hard block in 24 hours and a fully-cured structural element in 28 days.

Liquid concrete (typically Portland cement, water, sand, aggregate, ~10–20 percent paste by volume) placed in formwork and allowed to hydrate. Setting begins in 30–90 minutes; initial strength reaches in 24 hours; specified compressive strength is named at 28 days (typical structural mix is 25–40 MPa, high-performance concretes reach 80–150 MPa). Formwork is the dominant cost and craft variable: phenolic-faced plywood gives a smooth finish, board-formed plywood leaves a wood-grain texture, fabric formwork (a Mark West technique) gives organic curved shells, GFRC (glass-fiber-reinforced concrete) sprays into thin-shell molds. Reinforcement is rebar (typical) or fiber (steel, glass, polypropylene microfiber for GFRC) cast into the pour. Cure conditions matter — concrete poured below 5 °C needs heating blankets; above 30 °C needs evaporation control. Stripping the form too soon ruins the surface; too late fights the formwork release.

Scale & Tolerance

  • scale (mm)50 – 100000
  • tolerance (mm)5
  • skillbeginner can pour a stepping stone in an afternoon. Tilt-up panels and architectural exposed concrete demand a multi-trade crew (formwork carpenters, ironworkers, concrete finishers) and a foreman who has done it before.
  • costlow per cubic meter; high in formwork labor for one-off architectural work, low for repeated precast

Equipment

  • school_shopwheelbarrow or mixer (cement, sand, aggregate, water by recipe), formwork lumber + screws + form-release oil, vibrating poker (small) or hand tamping, rebar + tie wire + bolt cutters, screed board, trowels, curing blanket or burlap
  • professionalconcrete pump truck for high-rise pours, ready-mix delivery from a batching plant, motorized vibrators, helicopter trowel for slab finishing, custom modular formwork systems (Doka, Peri, Symons), tilt-up panel beds
  • industrialprecast plants with reusable steel molds, automated rebar placement, steam-cured fast-strip cycles, automated GFRC spray booths, 3D-printed concrete systems (Cobod, ICON) for site-printed walls

Environmental

  • energy_usehigh upstream (cement clinker production at 1450 °C dominates the embodied-carbon load — ~0.9 kg CO2 per kg cement); low at the pour itself
  • waste_streamwash-out water (high pH, regulated), formwork ply / lumber (often single-use for architectural finishes; reusable for utility pours), broken-out concrete (recyclable as crushed aggregate or road base)
  • consumablescement, aggregate, sand, water, form-release oil, rebar, tie wire, formwork ply (single- or multi-use)
Louis I. Kahn (dead — channeled)

I asked the concrete what it wanted to be, and the concrete said: I want to be a wall that shows my making. So I gave the concrete its formwork and its tie-rod holes and its joints between the panels, and I did not try to hide any of them, and the wall is honest because nothing about how it became a wall is missing from how it stands as one.

Channeled within the philosophy of Louis I. Kahn, *Louis I. Kahn: Writings, Lectures, Interviews*, ed. Alessandra Latour (Rizzoli, 1991); compare the formwork-and-tie-hole expression at the Salk Institute (1965) and the Kimbell Art Museum (1972).
Compatible materials
Portland Cement Concrete

Citations