The decorative effects being made on the surface of concrete are basically achieved in either of two ways: they can be applied at the forming stage before the concrete has hardened, or they can be applied to the finished concrete surface. There are a number of way decorative surfaces can be made. Probably one of the least expensive and least time consuming method is that of making use of the lumber used in formwork. Concrete board marked surfaces show the joint lines of rough or dressed lumber and often the grain impressions as well. Douglas wood is the most commonly used and all lumber should be sound, straight, and free from large loose lumps. To prevent excessive cupping, 6-d or 8-d common nails may be used. The second type is the use of plywood forms for textured and smooth faced surfaces. Some types feature a texture of deep, irregularly spaced, full length grooves for producing one way or vari-directional groove patterns. Where an especially smooth textured finish is desirable, it is some times advisable to use panels which have been smoothed with a plastic filler or lined with phenolic resin sheets. Similar to this is rubber form liners developed in England. Rubber sheeting of the desired pattern is placed at the bottom of the form or casting frame. Concrete is then placed over the sheeting, vibrated, and allowed to set. After it has set , the frame is removed and the rubber sheeting peeled away. Also in use are plastic form liners. The resulting finish will have a smooth, glass like quality. Another way to achieve a smooth appearance is through grinding tools. The third type is exposed aggregate surfaces. The simplest means of producing this effect is with the use of a chemical coating. The coating will retard the surface mortar and after the concrete has hardened the surface mortar can be washed away. To obtain a rough or dimpled surface, lay a layer of crushed rock and a sheet of plastic in between the concrete and rock in the form work. The fourth type is the use of stamping tools. The tools are actually platform walking units. By placing one tool in front or by the side of another, the user may walk over the surface of the concrete while he stamps a pattern on it. The fifth type is tools and materials for an applied finish. These often serve a functional as well as decorative use.