Although considerable depth of relief can be achieved with fiberglass forms, sculptured effects are usually achieved by applying a foamed or expanded plastic lining to the formwork. Sculptured with woodworking tools, or by burning out with hot wire or soldering irons, these linings are cheap, but cannot be reused. The fee of the artist to undertake the design is a significant part of the overall cost. Very heavily patterned reliefs can be produced by profiled formwork built up in plywood. Spectacular and bold shapes can be produced in this way.
Exposed-aggregate surfaces are usually used as decorative surfaces in their own right. Sometimes, however, they are used as contrasting areas in boardmarked or patterned surfaces. In such applications a bushhammer or other tool is usually used to expose the aggregate. The work of exposing the aggregate is done after stripping the formwork. Because this is an additional labor operation, it increases the cost to some degree. Exposed-aggregate treatments range from very light exposure to heavy relief textures. The resulting surfaces brighten from weathering. The same aggregate will also present a different color depending on the manner by which it has been exposed: an aggregate exposed by etching will appear different from the same aggregate exposed by bushhammering or even grit blasting.
Removing the outer skin of cement and fines with a bristle or wire brush while applying plenty of water exposes the coarse aggregate. Timing is vital it should usually take place two to six hours after casting, depending on materials and conditions. The operation can be done considerably later if a retarder is used. The retarder should be applied evenly to the formwork. It is important that the quality of the concrete must not be allowed to deteriorate merely because the surface is to be treated. Point tooling, bushhammering and chiseling are just three of the tooled finishes available.