Several manufacturers make cement-based backer boards for tiles, floors and countertops. These products include Portland Cement and sand. Some are glass-fiber-reinforced. Backer boards are installed in a manner similar to gypsum board. They are non-combustible and some types have a natural resistance to the growth of mold, which makes them good choices for wet areas. Lightweight Concrete Topping Several types of lightweight concrete mixtures may be used to cover floors. Some types are used to fill the spaces in corrugated steel decking. Others are used over existing floors to create a smooth, level surface to use as an underlayment for an applied floor finish. These toppings can also assist with limiting sound transmission from floor to floor and can add a noncombustible fire-resistant layer. Lightweight concrete toppings are used to pour over hot water tubes or electric heating cables in radiant-heated flooring applications. Some toppings have nylon fiber reinforcement and can be used as a wear layer. Designers can specify colored additives or the application of stain or paint as a finished floor. ALTERNATE USES OF CONCRETE Concrete Masonry Units Often erroneously called “cement blocks,” concrete masonry units (CMUs) are a form of precast concrete. Concrete is formed into molds, creating hollow blocks that conserve material and are lightweight. Concrete masonry units are relatively inexpensive and are used to construct walls using techniques similar to other types of masonry construction. Like concrete, the blocks are strong in compression but weak in tension. Thus, CMU walls are constructed with both horizontal and vertical reinforcement and the hollow spaces are filled with grout. The walls must be constructed so that the mass of the combined units acts as one entity. The main characteristic of concrete masonry units is their modularity. The standard CMU size is a nominal 8 x 8 x 16 inches but other sizes and shapes are available. Lintels, required to span openings in walls, correspond with modular dimensions of the CMU. Concrete masonry units are used to construct low-rise buildings and for interior walls that require fire separation, such as to enclose stairs, elevators, or mechanical rooms. Plain concrete masonry units are also used to provide a backup surface to attach brick or stone veneer walls on an interior or exterior. When exposed on an interior, plain CMU walls may be painted, or they may have furring strips and sheet rock applied. Alternatively, decorative CMUs can be used as an exposed surface, and may be colored and textured or ground smooth for a finished appearance. Types of Concrete Masonry Units In addition to the utilitarian plain gray concrete blocks, smooth-faced concrete blocks can have color added to the mix. The appearance of concrete masonry units is improved by adding color to the cement and exposing the aggregate, which can also be selected for a desired color. These more decorative CMUs are used to construct the exterior walls as well as i nterior walls of a building. Split-faced concrete masonry units have a textured appearance Concrete 91 92 Decoration 5 Decorating Gallery 5.4 Both Split-Faced and GroundFaced Concrete Masonry Units in an Interior: Lawrence High School Commons, Lawrence, Massachusetts. Photograph courtesy of Heidi Jandris that imitates natural stone. The stone-like texture is achieved by splitting the block so that broken aggregate is exposed. The surface also has a rough texture. Ground-faced concrete masonry units are made by grinding and polishing the surface of split-faced CMU, exposing the aggregate and giving the appearance of a polished stone or terrazzo. Both split-faced and ground-faced CMUs come in a wide variety of colors, depending on the color in the cement, the aggregate additives, and the pigment. They can be scored for a square appearance rather than the standard rectangle. Concrete masonry units can also be glazed, with an appearance similar to ceramic tile.
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Popular in the mid-twentieth century, screen blocks had open areas that allowed light and air to be transmitted. Screen blocks were used both on the exterior and interior as divider screens.
Textile Blocks: Frank Lloyd Wright In an effort to create something decorative out of concrete block, Frank Lloyd Wright developed the textile block, a square concrete block that he called “permanent, noble and beautiful.” The hollow blocks were textured on the outside. Steel-reinforcing rods tied the blocks together. The walls were built two wythes wide with a cavity air space for insulation. Frank Lloyd Wright designed four textile block houses in California in the 1920s, the Millard House in Pasadena, California (1923), the Storer House and the Freeman House (1923), and the Ennis House (1924) in Los Angeles. Each of the four houses had textile blocks with a different pattern. Decorating Gallery 5.6 Textile Blocks by Frank Lloyd Wright. Rusticated Concrete Block In the early twentieth century, from about 1905 until 1930, a popular style of concrete masonry units called rusticated concrete block, or rock-faced block, was formed in molds with a texture that mimicked stone. Portland Cement had become reliable, and Harmon S. Palmer had invented a hollow concrete block manufacturing machine that was sold through the Sears & Roebuck catalogue. The blocks could be made onsite with nonskilled labor. Rusticated concrete blocks were popular because they were less expensive than brick and stone, yet were fire-resistant. Rusticated blocks are still available for historic restoration and new construction. Cinder Blocks The popularity of cinder blocks began in the 1930s. The aggregate in concrete blocks was replaced with lighter cinders, which made the surfaces smooth. Application: Using Information Regarding Interior Finish Materials CODE ISSUES Concrete is a noncombustible material that can be used for the structural components of fire-resistant construction. However, steel used as reinforcement for concrete must be covered with prescribed thicknesses of concrete. For interior fire walls, fire barriers, and elevator and stair shaft enclosures, concrete or concrete masonry units are used to meet the required fire-resistance rating. Concrete 93 94 Decoration 5 Case STUDY of Concrete Used in an Interior Concrete Floors, Tables, and Reception Desks
Craig Shaw chose concrete to complement the industrial aesthetic of the former automotive repair building that is now the office of the decorating and design firm, Shaw Hofstra + Associates. Concrete topping on the floor was scored to create
Concrete is easy to maintain. Concrete floors, for example, can be damp mopped with a synthetic detergent. Avoid soap, which reacts with lime. Applying a sealer to the surface of a concrete countertop makes it easier to maintain.
Commercial buildings from the 1960s and 1970s were often constructed in the Brutalist style with exposed concrete walls. If this is the case, the walls may be left exposed as an interior finish. Concrete walls designed to be exposed may have intentional patterns from the formwork, such as plywood sandblasted so the grain is more pronounced, board pattern, or board and batten pattern. Special form liners can add textures such as ribbed patterns. After the concrete is cured, it can be acid etched, sandblasted, or bush hammered to add texture and expose the aggregate, or it may be ground smooth. Often the holes left by carefully placed form ties create a grid pattern on the surface.