How to Install & Apply Stucco to a Backer Board

Stucco applied to a house’s exterior creates a strong, weather-resistant coating.

While stucco can be applied directly to many surfaces, for maximum durability a specially designed backer board is usually installed against the existing wall.

1. Measure and cut backer board to fit the application. Score the backer board with the utility knife, place the scored line on a hard, straight-edge surface, such as the edge of a board, and push to snap off. Finish cutting the paper backing with the knife.

2. Attach the backer board with backer-board screws and a power screwdriver. For exterior walls, install backer board over foam-sheet insulation. Make certain the screws go at least ½ inch into the wall, past the board and sheet insulation.

3. Apply a cement bonding agent to the backer board and allow to dry according to the manufacturer's instructions.

4. Mix the stucco according to the manufacturer's instructions and apply a primary “scratch” coat with a trowel. Work in a straight line, one wall at a time, to minimize lines. Allow it to harden slightly and finish by smoothing with a plasterer’s rake. Allow the scratch coat to cure for 48 hours.

5. Dampen the scratch coat and apply final ¼-inch-thick finish coat with the finishing trowel. Texture as desired with a brush, sponge or trowel. Allow at least six weeks before painting.

Tip

Install pieces of foam, covered with fiberglass mesh, to hold the stucco in odd-shaped areas, such as around arches. Misting the stucco periodically (every three to four hours) for the first 24 hours after application will slow the curing process slightly, making it more stable once it is fully cured.

Warning

Do not use regular drywall screws to attach backer board as they are not designed to hold the weight.