How to have Concrete Paint to Stick to a Smooth Surface
Concrete paint won’t stick to a smooth concrete surface unless you first etch the surface. Etching creates microscopic depressions in the surface that provide it “tooth .” You can achieve this using a solution of muriatic acid or phosphoric acid, both of which are available at most paint stores. When the surface is etched, it is vital that you wait for it to dry, or you might wind up with bubbling and peeling paint. It’s a good idea to test the concrete for moisture before you prime and paint, particularly if the concrete is fresh.
Clean loose dirt and dust, either sweeping using a broom if it is a floor, or wiping with a dry rag. Wash the surface with a solution of 1 cup trisodium phosphate to 1 gallon of warm water to remove oil and grease. Rinse with clean water.
Don a respirator, goggles, rubber gloves and protective clothes. Etch an exterior layer using a muriatic acid solution, mixing it in a ratio of 1 part acid to 3 parts water. If the surface is indoors, use phosphoric acid, then mixing 1 part acid to 1 part water. Always add acid to water — never the opposite.
Transfer the solution to a garden sprinkling can to etch a floor. If you’re etching a wall, then use a pressurized garden sprayer. Evenly spread the acid solution over the whole surface and let it work for 2 to 10 minutes, or until the bubbling starts to subside, then wash it away with water in a garden hose.
Neutralize the acid by mixing a solution of 1/2 pound of baking soda per 1 gallon of water and spreading it over the surface with the same tool you used to spread the acid. Wash the surface with clean water.
Let the surface thoroughly dry. Before you paint, test it to make sure there’s no moisture seeping from underneath by taping a piece of transparent plastic down so it covers if not the whole surface, at least a big part of it. Leave the plastic overnight and look for condensation underneath it in the morning. If you see any, give the surface more time to dry.
Prime the surface with concrete primer before you employ concrete paint. The primer adheres better to the concrete than paint, and the paint adheres better to the primer than to concrete.