Concrete was invented by the Romans and has been used in construction for more than 2,000 years. Although some builders prefer to place a veneer -- such as brick or tile -- over a concrete surface, concrete can also have a number of finishes and textures. In addition, concrete coatings can provide color and sheen to a concrete floor or wall.
A continuous, smooth concrete wall or slab is pleasant to touch. Concrete's smoothness is affected by the method of casting, as well as the content of cement in the concrete mix. The higher the amount of cement, the smoother the finish on the concrete will be. Furthermore, concrete formwork with inconspicuous breaks gives a concrete wall a smooth surface. Each batch of concrete is different, so a wall made up of multiple pours will be visually striated. Although this is often undesired, some architects keep the striations to provide differentiation across a building's facade.
Surface Pattern and Troweling
Surface patterns can be created on a concrete surface by the concrete formwork, admixtures, cement content or troweling. Inserts can be placed within the concrete formwork to create surface patterns, such as ribbing or a repeated graphic. When the formwork is removed, the concrete surface has the inverse of the formwork insert. Architects often expose the concrete wall tie locations, which are necessary to hold the formwork together as the concrete cures. Also, admixtures can be added to concrete to retard the curing of the material, and the surface can be broomed as it cures to expose pea gravel aggregate. In addition, the cement content of the concrete can be diminished to expose the concrete aggregate in cured floors and walls. Finally, the concrete surface can be troweled to create texture variations, such as those found in stucco.
Bush Hammering, Blasting and Grinding
A cured concrete surface can be finished by degrading the surface of the wall or floor. Some options include bush hammering, which roughens the concrete surface; blasting, which erodes the concrete surface with sand or water exposing the aggregate and creating undulations in the concrete surface; and grinding, which gives a surface finish like terrazzo, exposing and polishing the aggregate at the concrete surface.
Most concrete formwork comes in modules that can be easily assembled and disassembled. Architects often try to show the way the wall is made by exposing the reveals or joints of the edges of the concrete formwork. In this way, the finished concrete surface is given a tiled or clapboard appearance, depending on whether the formwork is metal panels or wooden strips. The modules break down the facade, creating visual interest in the concrete surface and limiting the monotony of large expanses of concrete.
To seal the concrete and provide a higher sheen, many architects specify adding an epoxy coating to a concrete surface. The coating protects the concrete and also makes a shiny surface, almost like water. Sealing concrete is also helpful to tie a concrete surface together visually when there are multiple pours or types of concrete surfaces. The epoxy coating makes all of the concrete surfaces look as one.
Occasionally, architects specify a concrete color admixture that gives concrete a specific hue. The color is integrated with the concrete mix, so the concrete surface does not need to be painted. Although some fading occurs with color admixtures, the use of integrated color keeps maintenance costs down for concrete structures with this feature -- the building does not need to be repainted every few years.
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