Plywood for concrete shuttering work - Specification
2011 Edition

According to IS 4990:2011, plywood used for concrete shuttering should be of Boiling Water Proof (BWP) grade and preservative treated to withstand cycles of wetting and drying without degradation. The surface must remain hard and resist softening, checking, or cracking after 72 hours of boiling. Strength requirements include the capability to bear fresh concrete loads and endure forces from pouring and vibration. The plywood should also be reusable with proper handling, and strength properties may vary depending on timber species, as provided by manufacturers.

IS 4990 permits the use of any timber species for shuttering plywood, with Annex B listing preferred species. For ECO-Mark certified plywood, timber must originate from plantations or non-natural forests such as rubber, coconut, cashew, or shade trees from tea and coffee estates. The plywood must be BWP grade, preservative treated, and durable under wet and dry cycles. Manufacturers provide specific data on timber density and strength to ensure compliance and performance.

IS 4990 specifies several tests to guarantee water resistance and durability: a 72-hour boiling test where sample pieces are boiled continuously or intermittently and then evaluated for any surface deterioration; a wet bending strength test involving multiple boiling and drying cycles followed by immersion and mechanical testing per IS 1734 (Part 11). Minimum values for modulus of elasticity and rupture are specified for both along and across grain directions. Additionally, wood failure percentage and minimum failing load thresholds are set to ensure the plywood maintains structural integrity in wet conditions.

To prolong plywood life in concrete formwork, panels should be carefully handled to avoid surface damage—lifting instead of dragging, protecting edges and corners, and using waterproof interleaving during transport. Storage must be on flat, elevated, and well-ventilated surfaces protected from moisture. Maintenance includes applying mould oil before use and after multiple cycles, sealing cut edges with appropriate paints, ensuring proper drying by stacking with spacers when stored long-term, and regular cleaning and careful fixing of fasteners to avoid damage.

IS 4990 defines plywood thickness ranges based on the number of plies, for example, 3-ply sheets are available in 4, 5, and 6 mm thicknesses, while thicker plywood such as 9-ply or greater can range from 16 mm to 40 mm. The standard does not rigidly fix dimensional tolerances for length, width, and thickness, allowing these to be agreed upon between the manufacturer and purchaser. Typical tolerances include length variation of -0 to +6 mm, width of +3 to -0 mm, and thickness tolerances of ±10% for sheets under 6 mm and ±5% for thicker sheets. Edge straightness and squareness tolerances are also specified to ensure proper fit and performance.