What is concrete formwork and what is its function?
Concrete formwork is a temporary plywood or steel structure that retains fresh concrete until it cures and takes its final shape. It withstands lateral pressure up to 60 kN/m² for tall columns, holding the concrete for 7–28 days before stripping depending on cement type and temperature.
A formwork assembly has three components: the form face (plywood or metal), the timber or steel frame that supports it, and the shoring jacks that take vertical load. Design follows ACI 347 and SBC 201 to prevent collapse.
Formwork represents **40–60% of total reinforced concrete cost**, so choosing the right system and number of reuses directly drives project profitability.
What materials are used for formwork?
Formwork falls into four systems: 18 mm WBP Indonesian plywood (most common), phenolic film-faced plywood (15–25 cycles), steel forms (>100 cycles), and aluminium forms (lightweight for walls). Each system fits a defined project scale.
Towers and megaprojects: a mix of steel forms for columns and walls, with phenolic plywood for slabs. Residential buildings and villas: 18 mm Indonesian plywood with adjustable steel props.
Formwork accessories (tie rods, anchors, scaffold clamps, concrete spacers) are essential for stability. Choosing accessories per EN 12810 prevents form deformation during casting.
When should I choose plywood vs metal forms?
Choose plywood for medium projects (<2,000 m² casting), irregular shapes, and short-duration jobs. Choose metal forms for megaprojects (>10,000 m²), repeated columns, and high-rise towers. Metal forms cost 4–6x more but last 100+ cycles.
Economic break-even: above 30 reuse cycles, metal forms are cheaper in absolute terms. Below 10 cycles, Indonesian plywood is the optimal cost choice.
On Vision 2030 projects like NEOM and Qiddiya, contractors run hybrid systems: metal forms for repetitive walls, phenolic plywood for slabs and bespoke architectural shapes.
How do I size plywood thickness and prop spacing?
Thickness depends on lateral casting pressure = (concrete weight x pour rate x temperature factor). For columns at 1 m/h pour rate, pressure 25–40 kN/m² requires 18 mm plywood with vertical studs at 30 cm and horizontal walers at 40 cm. Steel props every 120 cm.
20 cm slab roof: 18 mm plywood on 5x10 cm timber joists at 30–40 cm spacing, with adjustable props every 120 cm. Total load 7–9 kN/m² covers concrete weight plus workers.
Walls: 18 mm plywood with horizontal walers at 40 cm and tie rods at 60 cm vertical. Exceeding these spacings causes form bulging and a deformed final wall.
How many times can plywood formwork be reused?
18 mm WBP Indonesian plywood reuses 5–8 cycles with form-release oil and horizontal storage. Film-faced phenolic plywood 15–25 cycles. Chinese plywood only 1–2 cycles. Steel forms 100+ cycles before replacement.
Factors that extend life: form-release oil before each pour, scraping off concrete residue with a plastic scraper, edge protection, and horizontal storage on bearers raised 10–15 cm above ground.
Field studies show each additional cycle cuts formwork cost per square metre by 12–15%, so investing in maintenance pays back economically for the contractor.
What are the common questions about concrete formwork?
18 mm WBP Indonesian plywood is the formwork standard in Riyadh, withstanding 45 kN/m² and reusable for 5–8 cycles. For megaprojects and exposed walls, phenolic film-faced plywood is better because it delivers a smooth, ready-finish surface.
Per ACI 347 and SBC 201: column sides after 24 hours, wall sides 24–48 hours, slab undersides 7–14 days, large beams 14–28 days. Premature stripping causes cracking and partial collapse.
Yes, Riyadh Timber offers phenolic plywood and steel props for rent for medium-to-large projects. Renting is economical when reuse exceeds 20 cycles, and includes delivery, retrieval, and routine maintenance.
Apply form-release oil to the form face before each pour using a roller brush at 250 ml per square metre. The oil creates a film that separates concrete from wood, easing stripping and preserving form life.
A standard shoring jack handles 2.5–4 tonnes safe working load at 3–4 m height. Concentric loading is essential; eccentric loading halves capacity. Prop layout is engineered against expected load.
WBP Indonesian plywood approved by Riyadh Timber complies with SBC 201 structural requirements, attached with ISO 9001 certificates and density and pressure test reports. These documents are submitted to the consultant before casting.
Need a formwork system designed for your project?
Send casting volumes and structural drawings, and our team will propose the optimal design (plywood/metal), quantities, props, and lead time with a formal quote within 4 hours.