Acid etching prepares concrete to bond with paint, an epoxy or a stain
Acid etching is the process of roughing up the slick surface of concrete with chemicals. Concrete can also be roughened with a grinder, but acid will do it with much less dust and muscle power. Acid creates tiny holes in the surface of the concrete, allowing it to bond with topical treatments such as paint, epoxy or stain.
Typically muratic acid is used to chemically treat concrete so that it can form the proper bond with topical surfaces. This concrete had metal flakes sprinkled on while the concrete was wet, then the surface was acid etched.
Acid combined with stain will etch and color the concrete at the same time. Applying stain can be tricky, and puddles and thin areas should be avoided to prevent the look from being mottled.
The longer the acid is left on the surface, the more porous the concrete becomes. Note the grainy pits in the surface of this kitchen floor. After etching, a neutralizer needs to be applied to stop the chemical reaction. Some acids time out so that neutralizer isn't necessary.
Even with a careful application of an acid or stain chemical, a natural amount of imperfection will result. A marble-like effect is created, because the acid is unpredictable. The result is a wonderfully unique surface.
Concrete also needs to be acid etched before you can apply epoxy. Epoxy is a polymer-based adhesive or paint that has a plastic feel to it. Thicker than paint, it has the benefits of being stronger as well as oil and heat resistant, and it fills in surface imperfections easier. Epoxy floors are common in professional garages.
The industrial look of this floor was created with an acid stain and the stubborn leftover adhesive from the original flooring. At times the best situations arise from accidents.
Acid stain comes in a variety of colors. Color can also be added by sprinkling pigment on the wet surface after the concrete is poured.
Whether the acid etching happens before the stain, epoxy or paint is added or not, the amount of sheen or gloss is determined by the clear topcoat. A high-gloss topcoat reflects light but also creates the most slippery surface.
This concrete floor was acid etched and then painted with a low-sheen paint, creating a matte look, and a topcoat was not used.