Timber should preferably be softwood, usually pine, chair, kail, bonsum, hollock, fir etc. which has been adequately seasoned before incorporation in the work. The choice of timber may also depend up cm local availability and cost. The timber is generally planed and should be able to held nails well.
Plywood is used as the sheathing material directly in contact with the concrete. When using either timber boards or plywood, it is usual 10 frame up the materials into the largest size of panel that can be handled by the available equipment on the site or is convenient for handling by men. Care needs to be taken during assembly, erection and casting so that their rather soft faces and edges are not damaged. Particular care is also necessary when striking off the formwork and during storage. Cut edges of ply and tie-holes should be sealed by aluminium paint or chlorinated rubber paint. This will prolong the life of the ply and tl?e number of times it can be re-used.
"Ballies" should be air dried to a moisture content not exceeding 20 percent within a depth of 12 mm form surface when measured at one third length of ballies form its butt end. They should be reasonably straight and shall be free from cuts across the grain, line, insect attack, any kind of decay, hollow heart and dead knots exceeding 5 cm in diameter. Ballies shall be so straight that when laid horizontally in any position, the centre line joining the apex and base shall not deviate from the actual axis of the ballies by more than 7.5 cm. The ballies should be cross-braced when used in scaffolding.
Steel
When the formwork has to be more than 4 metre high, it is better to go in for steel and tubular steel proprietary systems like Acrow and Doka. Since there are factory made products, therefore they are more reliable than wooden ballies. Steel shuttering gives more re-uses and has greater strength to weight ratio.
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