Formwork materials
can be classified as: 1. Timber 2. Metals 3. Plastics
1.Timber
a. Lumber:
- Lumber is commonly available material and has excellent strength, weight and cost factor.
- Lumber is classified as: • Boards: 1 to 1.5 inches thick, 2 or more inches width • Dimensions: 2 to 4 inch thick, any width. • Timbers: 5 or more inches thickness, 5 or more inches width
b. Plywood
- The use of plywood in concrete forming for form facing has improved the quality of finished concrete.
- The relatively large sheets of plywood have reduced the cost of building and at the same time have provided smooth surfaces that reduces cost of finishing of concrete surfaces.
- Plywood is a manufactured wood product consisting a number of veneer sheets, or plies
- Type of plywood can be grouped as exterior and interior. For formwork the exterior plywood is used. Adhesive used to bond the piles in manufacturing of exterior plywood is watertight and gives maximum number of reuses.
2. Metals
- The initial cost of metal formwork is more than timber formwork but the number of reuses of metal formwork is higher than that of timber.
- in long run metal formwork can be economical.
- İn heavy construction works metal formwork may require a lifting mechanism to handle the formwork panels or props.
- Steel sheet formwork has the problem of rusting also. To avoid rusting, in every use the surfaces should be oiled with an appropriate releasing agent.
- in metal formwork usage, the metal sheets are prepared as panels of standard sizes. This brings the difficulties of erecting irregular dimensions of formwork.
- Steel or aluminum or magnesium is the most widely used metals.
3. Plastics
- They have impervious surfaces that usually create a smooth finish to the concrete.
- Plastic formwork could be reinforced or unreinforced.
- Plastic is reinforced by glass fibers.
- Reinforced plastics are specially produced for a specific formwork type.
- Un-reinforced plastics are produced in sheet form with smooth or textured surfaces. • Plastic formwork is lighter but less durable than metal formwork.
See Also: Calculation of Loads and Pressures on Concrete Formwork