The formwork operations involve a number of activities including fabricating and erecting the forms, stripping, moving, and cleaning and oiling the forms for reuse. All of these activities and the materials involved are allowed for in the pricing of the forms. The estimator measures the surface area of the concrete that comes into contact with the forms; this is known as the contact area.
Because only the area of formwork is measured, the estimator does not have to be concerned about the design of the forms at the time of the takeoff. All that needs to be established is which surfaces of the concrete require forms. In the past, estimators have agonized over such things as whether the bottom of an opening or the sloped top surface of a wall needs to be formed. If discussion with your colleagues does not provide an answer, the prudent estimator will always exercise caution and allow the forms.
1. Formwork shall be measured in square feet of contact area; that is, the actual surface of formwork that is in contact with the concrete.
2. Formwork is classified in the same categories as those listed for concrete. As an illustration, consider a project with concrete footings, walls and columns, forms to footings; forms to walls and forms to columns would each be described and measured separately. There are, however, a number of factors which may have no effect on the price of the concreting operations but do affect the price of formwork and, therefore, should be noted. For example, the volume of concrete in all walls, whether they are straight or curved, will have the same price but the price of forms to curved walls will differ from the price of straight walls, so the forms to curved surfaces must be kept separate.
|Figure 1 Formwork Categories|
3. Bulkheads and edge forms shall be measured separately within these categories, so if there are construction joints required for long lengths of walls, the area of bulkheads to form these construction joints would be measured separately from the wall forms. Similarly, if there are pilasters projecting from the walls, the area of the pilasters would be calculated and noted separately from the wall forms. See Figure 1 for different categories of formwork in a wall system.
4. Forms to slab edges are measured separately from forms to beams and forms to walls, even where the edge forms may be extensions of beam or wall forms (see Figure 2).
|Figure 2 Types of Form|
5. Where there is an opening in a form system, no deduction is made from the total area of the forms if the size of the opening is less than 100 square feet (10 square meters). Examples of such openings would include openings for windows in walls, stairway openings, or elevator shaft openings in suspended slabs. The estimator must distinguish between what are openings and what are cut outs. Openings less than 100 square feet (10 m2) are not deducted but all cut outs would be deducted (see Figure 3).
6. Describe items of formwork that are linear in nature, stating their size and measuring their length in feet (meters). Grooves, chases, keyways, chamfers, and narrow strips of formwork less than 1 foot wide are measured in this fashion.
|Figure 3 Openings and Cut Outs in Formwork|
7. Describe forms to circular columns giving the diameter and measure in feet (meters) to the height of the column. Where columns widen at the top to form capitals, describe and enumerate these features. It can be useful to draw small sketches of complex items such as capitals to clarify exactly what is being measured. Include these sketches with the other takeoff notes.