Purpose
The purpose of joint compound is to finish drywall in a way that it looks and feels smooth. After drywall is finished with joint compound, a person sands it and paints the walls. Joint compound is also used to fill in nail holes or wall blemishes. Joint compounds contain several ingredients which may include limestone, water, perlite, dolomite, vinyl polymers and crystalline silica and is available in powder form, requiring you to mix it with water, or in premixed form.
Blue Vs. Green
People purchasing joint compound can often tell the difference in regular versus lightweight by the color of its container. Regular joint compound generally has a blue cover; while lightweight compound generally has a green cover. There are several key differences in these types of compound.
Lightweight Compound
Lightweight joint compound weighs less than regular and offers lower shrinkage. After applying any type of joint compound, it must dry before sanding it. When sanding it, lightweight compound is easier to sand than regular. It is used for all drywall needs, including covering joints, corner beads, fasteners and trim. Most of the time, lightweight joint compound requires only two coats, even when covering metal corner beads and fasteners. This type of compound is ideal for minor fixes in a home, but can be used for an entire drywall project.
Regular Compound
Regular joint compound is the original type of compound and is used for all drywall needs. It dries slower than lightweight compound because of its weight. If a worker applies too much of regular compound, it has a tendency to sag and is not used as often as lightweight compound for filling holes or cracks. Despite these aspects, regular compound is actually much harder than lightweight compound after it is dried. Because of this, it often holds up better and is preferred by many drywall contractors. Skilled drywallers normally know how much compound to apply to prevent it from sagging.