How Much Sand Is in Stucco?

Basics

• Stucco, sometimes called Portland cement plaster is generally made out of Portland cement, sand and water. Hydrated lime is also needed so the plaster is easy to spread and sticks to lath on walls. To minimize the number of ingredients, contractors can use plastic cement. This eliminates the need for lime, since plastic cement is workable as formulated. Most plasterers prefer the latter formulation, though a few mix equal parts of plastic and regular cement, and some use regular cement, especially when trying to match older stucco on a vintage home.

Types of Sand

• Plasterers can use three types of sand from a home center or dry material yard. First is concrete sand. Its coarseness makes good quality plaster but is hard to spread. Second is masonry sand, which is too fine for use in base stucco coats because it can produce cracks in the plaster. Third is plaster sand, which allows spreadability but is coarse enough to avoid cracking. It must be clean and correctly graded. When delivered to the home site, it requires protection from dirt, oil, grease, leaves and debris.

Recipes

• The actual sand required by stucco depends on use. For mixtures with Portland cement, the recipe for the first or scratch coat is the thickest. It requires one 94-pound bag of cement, 0.33 16-pound bags of type-S hydrated lime and 4 cubic feet of loose, damp plaster sand, which is equivalent to 5.33 5-gallon buckets. The secondary brown coat requires 10 percent more hyrdrated lime and sand. The finish coat needs one 94-pound bag of white Portland cement, 0.5 25-pound bags of type S hydrated lime and 5 cubic feet of loose damp plaster sand, which equals 6.67 5-gallon buckets. Any coloring is usually added to this finish coat.

Mixing

• Plasterers generally start by pouring some water into the mixer and then part of the sand. Then come one or two bags of cement, depending on the size of the mixing machine, followed by the lime. More water is needed, and then the rest of the sand, followed by water to keep the mix workable. Workers must carefully gauge the amount of water needed because too much can weaken the stucco and form cracks. Mixers should stir the plaster for at least four or five minutes to allow the air bubbles to make the concrete flow. Lime introduces air entrainment into Portland cement. For plastic cement, the air entrainment agent is part of the mix.