Requirements of good formwork

1. It should be strong enough to resist the pressure or the weight of the fresh concrete and the superimposed loads due to equipment, men etc., if any. This requires careful design of the formwork, because the consideration of overloads will affect the economy whereas of under loads may cause failure of the formwork.

2. It should be rigid enough to retain the shape without undue deformation. Therefore, it should be so designed that deflection does not exceed 1/900th of span in normal cases.

3. It must be made or constructed as tight so that it does not allow the cement paste to leak through the joints.

4. The space enclosed by the form should be true to the size as designed. The form should, therefore, not warp, bend, bulge or sink to meet this requirement.

5. The inside surface of formwork should be smooth so as to give good appearance to the resulting concrete surface. To achieve this, the inside surface of formwork is usually applied with crude oil or soft soap solution. This also facilitates the removal of formwork.

6. The entire formwork should be so made that it can be removed easily without causing the least injury to the surface or edges of the concrete.

7. As the formwork does not contribute anything to the stability of the finished structure, it should, therefore, be made economical by reducing the cost through proper design, construction and use of proper material.

8. It should be as light as possible. So that it is easy to transfer.

9. The material of the formwork should be cheap, easily available and should be suitable for reuse.

10. Self-weight of the form work should be less.

11. It should be easily possible to give the required geometrical shape to the form.