What Is a Drywall Compound?

All-Purpose Drywall Compound

• All-purpose drywall compound is commonly used to embed the drywall tape in the seams where two different pieces of drywall meet or when you apply a textured top coat to the drywall. When all-purpose compound dries, it is much harder than the other compounds, which makes it more difficult to sand. Of the three varieties, this one shrinks the most as it dries.

Topping Joint Compounds

• Lightweight joint compound is easy to apply and often used during the first and second application of compound. As it dries, there is minimal shrinkage and because of its lighter consistency, it is much easier to sand when it dries. When first opened, a bucket of lightweight joint compound will have a significant amount of air bubbles in it, so you should slightly mix it with a taping knife to work out the air and help ensure a smooth application on the wall.

Quick Set Joint Compound

• While all-purpose and topping joint compounds most commonly come premixed in 5-gallon buckets, quick set joint compound most often comes as a powder in bags. You must mix the powder with water, according to the manufacturer's specifications, to achieve the proper mud-like consistency. Once dried, quick set mud has the hardest finish and closely resembles plaster. Quick set mud does just that, beginning to harden in as little as five minutes after you mix it.

What's In Drywall Compound?

• No matter what type of drywall compound you're using, they all consist of the same basic ingredients. They include gypsum, limestone, dolomite and water. Depending on the manufacturer's formula, it may also contain mica, a silicate mineral, and vinyl acetate, a polymer.