What Is a 3-Coat Stucco System?

Exterior Finish

• Stucco is usually applied as an exterior finish; a comparable material used in interiors is called plaster. Stucco can be applied to almost any wall covering. It can go directly on poured concrete or concrete-block walls, brick or other masonry. It is secured on wood-sheathed walls with metal lath, thin metal with holes in it nailed to the wood. Most stucco still follows the traditional three-coat pattern. Stucco can be colored when applied, or painted later.

Scratch Coat

• The first layer of stucco is called a scratch coat. It is spread over the wall with a trowel, usually a flat type with a smooth bottom, one straight edge and one edge with notches along it. The stucco is spread 1/4 to 1/2 inch thick with the flat base of the trowel, allowed to set up slightly, then scratched with the notched side of the trowel or a corn broom to create horizontal ridges along the wall. That coat is allowed to cure for 36 to 48 hours.

Brown Coat

• A second coat is called a brown coat, taking its name because sand is usually added to the stucco mix to provide a rougher surface for a finish layer to bind to. The brown coat also is applied with a flat trowel in a generally smooth fashion. Once the wall is covered and stucco starts to set, it is smoothed with a screed, a long wood or metal tool pulled down the surface to even out the stucco. This coat is 1/8 to 3/8 inch thick. It also is allowed to dry.

Finish

• A finish coat gives stucco its final texture. It generally is thinner, 1/8 to 1/4 inch thick, but for a rough texture can be applied thicker. This coat is finished to any desired texture. It can be smoothed with a trowel to an almost perfectly flat surface, roughed up with the trowel to create irregular peaks and valleys, or given a special treatment by letting it set a bit with small peaks, which then are smoothed slightly with the trowel edge to look like popcorn or cottage cheese.