BOHGUN RENOVATIONS plastering new surfaces, all masonry joints should be racked to a depth of 10 mm in brick masonry and 15 mm in stone masonry for providing key to the plaster. All mortar droppings and dust and laitance (in case of freshly laid concrete) should be removed with the help of stiff wire brush. Any unevenness is leveled before rendering is applied. For finishes applied in three coats, local projections should not be more than 10 mm proud of general surface and local depressions should not exceed 20 mm. For two coat plasters these limitations are 5 mm and 10 mm respectively. The surface should be washed with clean water and kept damp uniformly to produce optimum suction. In no case the surface should be kept soaked with water so as to cause sliding of mortar before it sets or kept less wet to cause strong suction which withdraws moisture from mortar and makes it weak, porous and friable. If plaster is to be applied on old surface, all dirt, scool, oil, paint etc. should be cleaned off. Loose and crumbling plaster layer should be removed to its full thickness and the surface of the background should be exposed and joints properly racked. The surface should be washed and kept damp to obtain optimum suction.