Whether you need to patch up a small hole or paint a new wall, choosing the right joint compound, also referred to as drywall compound or drywall mud, is a key step in order to prepare drywall for proper painting. The joint compound is a water-based paste that helps generate a continuous surface and keeps paint looking smooth and uniform throughout the wall. However, with so many types of joint compound to choose from -- from quick-setting to pre-mixed -- picking the right kind can be a bit tricky.
Pre-Mixed Joint Compound
The pre-mixed joint compound is the traditional type of drywall mud. Pre-mixed typically comes in buckets and is already mixed and ready to be applied. Even though it's ready to go out of the bucket, it's often recommended to thin out the pre-mixed joint compound with a little bit of water. This will help with the application and ensure that the compound goes on uniformly. Pre-mixed drywall mud comes in three main kinds: light-weight, all-purpose, and topping. One thing to keep in mind with any type of joint compound is that typically more than one type is used on the same wall. This is true because some compounds are better for the first coat while others are great for finishing. Therefore, using them in conjunction with each other is often beneficial.
Lightweight Joint Compound
The lightweight joint compound is a type of pre-mixed mud that is great for filling in small holes or cracks in a wall. Lightweight mud normally does not have sagging issues after it has dried, which makes it great for patchwork. It's also very frequently used as a finish coat because it's really easy to sand compared to the other premixed muds. However, many professionals don’t choose to use lightweight formula as a first or second coat because it isn’t as strong as heavier-made compounds. If it is used as a first coat, then it's recommended to use tape with it to help strengthen it.
All-Purpose Joint Compound
Just as its name implies, an all-purpose joint compound is made for all kinds of applications, from bedding in tape to finishing work. This kind of mud dries very hard, so it tends to be more difficult to sand down as a finish coat. However, because of its durability, some do prefer to use it as a finish coat. One thing to keep in mind with this mud is that it takes a long time to fully dry. Additionally, because it is a heavier mud, if it's not applied right it can sag and therefore is not recommended for small holes unless the tape is applied.
Topping Joint Compound
Topping joint compound is another type of pre-mixed joint compound and is used primarily to top off seams and corner beads. This type of compound is not as frequently used as lightweight or all-purpose types of joint compounds, but it is easy to sand. It's also much whiter than any other mud and is often applied as a texturing agent. Additionally, the topping compound can be used as a first or second coat and is great for this purpose because it does not tend to shrink as much as other types of mud.
Quick-Setting Joint Compound
A quick-setting joint compound is very different than traditional pre-mixed drywall mud. In contrast to traditional muds, quick-setting comes as a powder and needs to be mixed with water. It's usually packaged inside a plastic lining, and after water is added a chemical reaction occurs and it's ready to use. Manufacturers sell quick-setting compounds with different hardening times, from 5 minutes to 45 minutes, which makes this kind of mud ideal if time is an issue. The downside of quick-setting mud is that it can be difficult to sand down, and therefore isn’t normally used as a finish coat. Additionally, since this type of compound dries very quickly, once it starts setting there is less time to make sure everything is in proper order.