When properly applied, stucco has many of the desirable properties of concrete: it's hard, strong, economical, and durable in both warm and cold climates. THE RIGHT INGREDIENTS Stucco is a mixture of cement, sand, and enough water to make it workable. Designing the mix can be more of an art than a science and usually is based on experience with local materials. You can use portland cement (gray or white), masonry cement, or plastic cement. Because stucco is mostly sand, a good-quality aggregate is critical. Aggregates should conform to ASTM C 897. Many types of admixtures can be used in stucco: air-entraining agents, accelerators, water repellents, bonding agents, and pigments. MIXING Don't mix stucco by hand. Mixers produce more consistent batch-to-batch mixes. After all the ingredients are added, continue mixing for 3 to 5 minutes. Add water, if necessary, to obtain the consistency wanted by the plasterer. IS REINFORCEMENT NECESSARY? Expanded metal lath is needed if the masonry surfaces can't provide adequate bond, can't be prepared economically for direct application of stucco, or if extra-thick or high-strength stucco is required. When metal lath is used, it's often installed with backing paper. TWO COATS OR THREE? Generally, stucco is applied in two or three coats. The choice depends on the wall surface and the climate. For a durable stucco finish, follow ASTM requirements for the thickness of each coat.