The application of a cement mixture for the primary purpose of making lightweight concrete walls watertight is known as rendering. It serves also to provide smooth, easily maintained and nonabsorbent interior surfaces and to enhance the appearance of a structure. Rendering aims to achieve such physical properties as durability, resistance to moisture penetration, and uniform weathering. A basic mix for rendering is 6 parts well graded sand to 1 part cement and 1 part lime. Portland cement or portland blastfurnance cement should be used. An alternative mix of 1 part masonry cement and 5 parts sand may also be used. The first step is to prepare the surface so that it will provide a good key to support the rendering. The application of a stipple coat is necessary to prepare a wall with aerated or water-absorbent blocks. The rendering mix should be highly workable and cohesive. The first coat should have a maximum thickness of three-eighths of an inch. Thickness can be regualted by fixing three-eigths of an inch wood battens to the wall. After the coat is applied, it can be screeded with a straingtedge. The second coat should have a maximum thickness of one-fourth of an inch. If the first coat is properly dried and cured, the finished rendering is less susceptible to cracking through shrinkage. The second coat can be finished with a wood float to produce a gitty surface. Painting the surface is the final step, either to produce a decorative finish or to obtain additional resistance to chemicals. Paint manufactures' instructions should be followed carefully in all cases.