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GYPSUM PLASTER

Gypsum plaster is primarily composed of calcium sulfate, a mined mineral. Until the advent of drywall (gypsum wallboard), gypsum plaster was widely used as an interior wall finish in the United States and Canada. It was usually applied over wood lath — wood slats nailed horizontally onto wall-framing members. But as the popularity of drywall skyrocketed, gypsum plaster fell out of favor. It is now rarely used in conventional home construction, except as a decorative coat over drywall to produce texture and interesting patterns. In the interiors of many natural homes, however, gypsum plaster is experiencing a revival.

Gypsum plaster is widely available, relatively inexpensive and easy to work with. You can purchase it in dry-powder form from many building-supply outlets. Powdered mixes require only the addition of water and a little stirring before application.

Gypsum plaster goes on quickly and adheres well to a variety of surfaces. It is usually applied in two coats: a base coat and a finish coat. Because it sets up quickly, application of the final coat proceeds soon after the first coat is laid down.

Another benefit of gypsum plaster is it expands slightly as it dries I and sets up, which reduces or eliminates cracking. Most other plasters shrink a bit when curing and are more prone to cracking. Although hairline cracks may form in gypsum, daubing cracks with a wet cloth or sponge seals them.

Gypsum plaster sets quite hard, producing a durable interior-wall and ceiling finish. Like lime plasters, gypsum plasters require little maintenance. Most finish gypsum plasters can be wiped clean if soiled and are not subject to dusting or crumbling.

But gypsum has its disadvantages. Although it provides a durable interior surface, gypsum plaster is too water soluble to use on exterior walls. Because it sets up so quickly, it is difficult for beginners to work with. In addition, gypsum contains a number of chemical additives to improve set time and hardness. These volatile organic chemicals outgas from the material both during application and after the plaster dries, and may be of concern for chemically sensitive individuals.

CEMENT STUCCO

A mixture of portland cement, sand, fiber and small quantities of lime, to permit it to expand and contract without cracking, cement stucco provides a durable finish for exterior walls. Cement stucco has a long history of successful application in a wide variety of climates, from the arid deserts of Arizona to the frigid forests of Wisconsin. This tough exterior finish can be pigmented or painted to achieve a wide variety of beautiful colors. Cement stucco may last a building's lifetime if applied correctly.

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