How to use stucco over foam board
Stucco is a wall-finishing material comprised of Portland cement, sand and lime applied in two to three coats over walls. Stucco has hundreds of years of history, though its traditional, labour-intensive techniques have led to more modern, synthetic methods.
Part of the synthetic method includes using a polystyrene foam board as a base attached to the wall base, which is often made of plywood. The stucco is then laid using a base and mesh to effectively adhere the cement mixture to the board.
Fit the acrylic mesh over the foam base so the mesh is the same length and width as the wall. Cut any excess away.
Secure the mesh in place with roofing nails. Roofing nails are longer than regular nails and designed for durability, so they will withstand the application and pressure of the stucco.
Mix the cement-stucco base according to the manufacturer's instructions; stucco may come premixed or require the addition of water. Mix the stucco in the bucket to a uniform consistency.
Apply the cement-stucco base to the foam base over and through the mesh using a trowel. Create a 1/2-inch thick layer. Allow this layer, called the "scratch coat," to cure for 36 to 48 hours.
Mix the finishing coat of stucco in a bucket according to the manufacturer's instructions. Apply the finishing coat to the cured scratch coat with a trowel. This outer coat should be anywhere from 1/8- to 1/4-inch thick. Allow the finishing coat to cure for three to four days, misting it with a water hose daily to prevent it from drying out.
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