If you would like to apply paint over a rock wall, you will need to prepare the surface a particular way, prior to application. Because rock walls are poorly suited for adhesion, you must condition them with a base coat of primer, or they will eventually shed their new finish. In addition, you need to select the appropriate type of paint based on the location of the wall, or you may end up with an unattractive finish that will fail over time.
Things You'll Need
Coarse plastic brush
Heavy-duty fabric drop cloth
Blue painter's tape
Nap roller cover
3- to 4-inch latex paintbrush
Acrylic latex paint
Satin or semi-gloss latex paint
Clean exterior rock walls, using a pressure washer. Use wet rags and a coarse brush if the wall is located indoors. Wait one to three hours for the clean rock wall to dry.
Cover surfaces below the rock wall with a fabric drop cloth. Cover areas on and adjacent to the rock wall that you do not want painted with a low-tack painter's tape.
Coat the clean rock wall with primer. Use a latex primer if the rock wall is located indoors. Use an acrylic latex primer if you are working on an exterior rock wall. Roll the primer onto the rock wall. Apply primer to areas of the wall inaccessible to the roller using a paintbrush. Wait two hours for the primed rock wall to dry.
Wash the painting tools with water.
Coat the primed rock wall with paint. Use a satin or semi-gloss latex paint if the rock wall is located indoors. Use an acrylic latex paint if you are working on an exterior rock wall. Apply paint to the wall just as you did the primer. Wait two hours for the painted wall to dry. Add another coat if you can see the primer showing through.
Do not paint over an unprimed rock wall, or the finish will fail.
Do not use ordinary latex paint on an exterior rock wall, as it lacks the elasticity necessary for contracting and expanding in varying temperatures.
If you need to use a ladder to access higher portions of the rock wall, read the safety guide printed on the side of the ladder before you begin work.