Lightweight joint compounds are ideal for drywall repairs on vertical surfaces.
Conventional drywall joint compound does its job well, but in some applications its weight and tendency to sag while drying are disadvantages. Lightweight joint compounds avoid that disadvantage but create a few of their own. Knowing the differences between the type of lightweight compounds can help you choose the ideal product for your job.
Lightweight Vs. Conventional Weight
As the name suggests, lightweight joint compound is chemically formulated to weigh less than conventional compounds. The actual weight savings vary from product to product, but manufacturers typically claim that their lightweight products weigh 20 to 30 percent less than their conventional products. DAP, for example, says its Premium Lightweight Joint Compound weighs up to 25 percent less than conventional compounds. USG claims its SHEETROCK AP Lite compound weighs up to 20 percent less than its All-Purpose compound.
Drying-Type Compounds
Drying-type joint compounds are typically vinyl-based powders mixed with water. These compounds harden as the water evaporates and dry more slowly than setting-type compounds. Drying times are longer when temperatures are low or humidity is high. Drying-type compounds, unsuitable as a first coat over fiberglass joint tape, are generally easier to sand and can be kept from drying out by adding more water to them. This extends the time that the compound remains workable. Lightweight drying-type compounds include USG's SHEETROCK Lightweight All-Purpose, SHEETROCK Plus 3, SHEETROCK AP Lite and DAP's Lightweight Wallboard Compound.
Setting-Type Compounds
Setting-type joint compounds are formulated to use a chemical reaction that dries faster than drying-type compounds. Most compounds will dry in 20 minutes to six hours, and drying times are not affected by temperature and humidity. Disadvantages of setting-type compounds include the inability to stop the drying reaction once it starts and the relative difficulty of sanding the setting-type's harder surface. Lightweight setting-type compounds include USG's BEADEX Silver Set compound and SHEETROCK Easy Sand Lightweight.
Advantages and Disadvantages
Beyond their obvious weight advantages, lightweight compounds also tend to have a firmer texture than conventional compounds, making them better suited for making repairs on vertical surfaces. They also tend to shrink or sag less and are easier to sand than conventional compounds. The surface of conventional compounds tends to be harder and more durable than lightweight compounds.
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