Copyright Goodheart-Willcox Co., Inc. 396 Section 5 Concrete Concrete faithfully reproduces the wood texture, and the rough board appearance tends to hide tie rod holes and other imperfections. Use one of the following methods to ensure uniformity of surface texture: • Use lumber of the same type throughout. • Use a form coating to seal the surfaces of the boards. • Bush hammering produces a coarse concrete texture. This is a method of mechanically breaking away the wall surface of hardened concrete to expose coarse aggregate. Interesting color variations and surface textures are produced by bush hammering. Ve rtical fins or ribs can produce shadow effects on a concrete wall. See Figure 18-35. The fins can be smooth, sandblasted, or hammered. Inserts of wood, metal, or plastic can be used to create the ribs. See Figure 18-36. Grid-Patterned Concrete Walls Well-planned joint patterns provide a low-cost architectural treatment for cast-in-place walls or other structural elements. Construction joints can be inconspicuous or hidden by rustication strips. These strips produce grooves in the concrete surface, which add something to the overall architectural effect and serve as control joints. Removable architectural ties can be used to provide minimum-size, easily patched holes, or the tie holes can be accentuated to reduce cost and enhance the appearance. When form joints and tie holes are left unfinished, they are placed at predetermined locations and the pattern is repeated throughout the structure to create an architectural effect. See Figure 18-37. Colored Aggregate Surfaces One of the best methods of obtaining color in a cast-in-place concrete wall is through the use of exposed aggregate. A large percentage of coarse aggre- gate is used in the mix. The surface is sandblasted, bush hammered, or chisel-textured to expose the colored aggregate. Goodheart-Willcox Publisher Figure 18-34. This wall texture was the result of using rough sawn form boards. The tie rod holes add to the overall texture effect. Goodheart-Willcox Publisher Figure 18-35. Fins or ribs on concrete add interest to the design of a structure. American Plywood Association Figure 18-36. This concrete ribbed surface has been hammered to expose the aggregate.