Stucco is an exterior finish made from a mixture of Portland cement, lime, and sand. It can be applied to masonry or frame walls. In new construction, stucco is often used as both the finish material and the weather barrier. To apply stucco, a scratch coat (a thinned-down mixture of cement and water) is first applied to the wall. The scratch coat should be thin enough so that you can still see the underlying surface through it. After the scratch coat dries, a second coat called the brown coat is applied.

You put a moisture barrier under stucco. A moisture barrier is either a self-adhesive membrane or asphalt felt paper. The membrane or paper goes over the sheathing and is lapped up the wall at least 6 inches. You also need to install weep holes (vertical drainage openings) in the foundation wall and in the bottom course of masonry veneer, so that any water that gets behind the stucco can escape.