The concrete should be placed and compacted before setting commences and should not subsequently be disturbed. Method of placing should be such as to preclude segregation. Before concrete is placed, it should be ensured that forms are rigid, in their correct position, well cleaned and oiled. Oiling of the forms will prevent the concrete from sticking to it, and it will then be easier to remove the forms when they are no longer required. Concrete should not be poured into the forms only at one point, but should be uniformly spread on all sides for better compaction. When the work has to be resumed on a surface which has hardened, such surface should be roughened. It should then be swept clean, thoroughly wetted and covered with a 13 mm layer of mortar composed of cement sand in the same ratio as the cement and sand in the concrete mix. This 13 mm layer of mortar should be freshly mixed and placed immediately before the placing of concrete. Where the concrete has not fully hardened , all lattence should be removed by scrubbing the wet surface with wire or bristle brushes , care should be taken to avoid dislodgement of particles of aggregate. The surface should be thoroughly wetted and all free water removed. The surface should then be coated with neat cement grout. The first layer of concrete to be placed on this surface should not exceed 150 mm in thickness and should be well – rammed against old work, particular attention being paid to corners and close spots.
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