- 1). Prepare the concrete wall. If the wall has been painted and the paint is peeling or flaking, all of the paint has to be removed. The easiest way to do this is to have the wall sandblasted.
- 2). Install metal lath over the painted concrete wall if you don't want to sandblast. Use 7/8-inch concrete screws with washers spaced 12 inches apart to attach the lath to the wall.
- 3). Caulk any cracks and treat mold and mildew by first killing the mold and then removing any stains left by the mold. Clean mortar joints with a wire brush.
- 4). Use a bonding agent on painted walls, when the paint is securely bonded to the wall. Spray or brush the agent over the entire wall. Follow the manufacturer's instructions.
- 5). Apply a dash, slush or slurry coat to the concrete wall. Mix 1 part Portland cement, 1 to 2 parts of masonry sand and enough water to create a runny consistency. Use a dash brush to cover the entire wall to a thickness of about 1/8 inch. Let the slush coat dry for a day. Dash, slush and slurry all refer to the technique of creating a base coat. For a very flat finish, use a slurry that is almost liquid in consistency.
- 6). Mix plaster according to the manufacturer's instructions. Apply a base coat over the dash coat that's between 1/4- and 3/8-inch thick with a trowel. Smooth the plaster out for a flat wall. Leave the wall rough for a textured look. Let the base coat dry.
- 7). Put a second coat of plaster over the base coat using the same technique and plaster mix.
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