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Acid stain is a method for adding color and variety to ordinary concrete. Like wood stain, concrete acid stain is not a surface treatment; it penetrates into the concrete, creating a permanent color change. It is generally made with hydrochloric acid, metal or mineral salts, and water. The most popular application for acid stain is to beautify interior and exterior concrete floors, but it can be used to finish a variety of concrete structures including walls, pools, and patio furniture. Additional artistic effects can be achieved by etching patterns or designs into the concrete with a fine saw before or after staining.
Acid stains work by chemically interacting with the minerals found in the concrete. The acid opens the surface of the concrete and allows the metallic salts to penetrate deep into the pores. The metallic salts then react with the limestone found within the concrete; the water in the stain also facilitates this reaction. Different colors are produced by different metals found in the stain, as well as the addition of tints and dyes. The acid must then be neutralized to halt the reaction and stabilize the color before sealing.
Application of concrete stain is a multi-step process that is often handled by experienced concrete professionals. The surface must be thoroughly cleaned, and any chips or holes repaired. The acid stain is then applied with a sprayer and worked into the concrete with a stiff-bristled floor broom or scrub brush. After sufficient time for the color to develop, the acid is then neutralized with a solution of baking soda and water and the residue removed with mops and wet vacuums. After the concrete has dried completely, a clear sealant is usually applied to protect the floor and preserve the color.
The finished look of acid-stained concrete is varied and mottled because of the natural variations in the concrete itself. Sometimes resembling marble, acid-staining is highly popular because of this variation; no two floors ever look exactly alike. Color choices in acid stain used to be limited to shades of bronze, brown, black, and blue-green; this reflects the range of metals used in acid stains and the chemical reactions they produced. With the addition of translucent tints and dyes, concrete stain can now be found in a much wider range of colors, including lighter shades such as yellow. Tints and dyes also help provide more even color by staining areas of the concrete that did not react with the metallic salts.
Stained concrete floors are sometimes made even more beautiful with patterns and designs etched into the surface. Artistic touches can be as simple and striking as a bold block or checkerboard design, or as intricate as delicately etched animal or floral patterns. An experienced concrete artist, with a wide variety of stains to choose from, can transform a dull concrete floor into a stunning work of art.
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