Red Seal Drywall Finisher and Plasterer Practice Exam

The primary ingredient in joint compound is gypsum. Gypsum is a mineral that is primarily composed of calcium sulfate dihydrate. In the context of joint compound, gypsum is ground into a fine powder and mixed with water, along with various additives, to create a smooth, workable paste that can be applied to drywall seams and imperfections. The use of gypsum in joint compound is crucial as it provides the desired properties such as the ability to adhere to surfaces, ease of application, and a smooth finish once dried.

The other options do not serve as the main component of joint compound. Calcium carbonate is often used in other types of products, but it does not provide the same properties as gypsum in joint compound. Cement is a binding material used primarily in concrete and does not relate directly to drywall finishing processes. Silica may be present in some formulations but is not the main ingredient; instead, it adds texture and affects drying times in different kinds of compounds. Understanding that gypsum is central to joint compound helps clarify its unique role in drywall finishing.