Painting is one way to spruce up your drab basement, patio or porch concrete floor. Hide the blemish left behind after repairing a crack or just add color to the space with concrete paint. However, concrete is a difficult surface to paint unless it is properly prepared. The prep work can be time-consuming, but preparing the surface properly will ensure a long-lasting finish.
Preparing concrete for painting is all about improving the surface to accept the paint. Paint does not adhere to fresh concrete. Allow the concrete to cure at temperatures of at least 75 degrees Fahrenheit for at least 30 days. Clean the surface thoroughly, removing dirt, oil, grease and any other substances that may prevent the paint from adhering to the concrete. Fill holes and cracks with a cement patching compound.
Etching the surface of the floor opens the pores in the concrete again to improve the paint adhering to the concrete, especially on smooth, glossy surfaces that may repel the paint. Shot blasting and acid etching are the two methods commonly used to prepare the surface for painting. However, shot blasting requires special training and equipment and is left to the professionals. For acid etching, a muriatic (hydrochloric) acid solution is spread on the concrete and brushed across the surface with a floor machine equipped with nylogrit brush used for etching and then is rinsed away. If done properly, the etched concrete will feel like 80- to 100-grit sandpaper.
In addition to creating a rough surface for the paint to adhere to, acid etching removes salts from the surface and neutralizes the pH level of the concrete, factors that prevent the paint from sticking to the concrete. If you choose to skip the etching step before applying the paint, the paint may bubble up, peel or flake off the concrete, especially on smoothly finished surfaces, leaving the surface more unsightly than before you painted.
Wear protective gear when acid etching your concrete floor. Etching is normally a two-person operation with one person applying the acid and the other working the floor machine. Work in 150-square-foot sections, rinsing the sections thoroughly with water followed by a neutralizer and more water. The acid solution is corrosive to aluminum and painted metal. Protect aluminum doors and other metal objects during the etching process. Allow the floor to dry completely before painting, waiting a couple of days if necessary.