Drywall mud, also called joint compound, is a gypsum-based paste used to finish drywall joints and corners in new drywall installations. It's also handy for repairing cracks and holes in existing drywall and plaster surfaces. Drywall mud comes in a few basic types, and each has its advantages and disadvantages. You may choose one type for your project or use a combination of compounds for the desired results.
What Is Joint Compound or Mud?
Joint compound, commonly called mud, is the wet material that is used for drywall installation to adhere paper joint tape, fill joints, and to top paper and mesh joint tapes, as well as for plastic and metal corner beads. It can also be used to repair holes and cracks in drywall and plaster.
Types of Joint Compound
All-Purpose Compound: Best All-Around Drywall Mud
Professional drywall installers sometimes use different types of muds for different stages of the process. For example, some professionals use a mud just for embedding paper tape, another mud for setting a base layer to cover the tape, and another mud for topping the joints.
All-purpose compound is a pre-mixed mud sold in buckets and boxes. It can be used for all phases of drywall finishing: embedding joint tape and filler and finish coats, as well as for texturing and skim-coating. Because it is lightweight and has a slow drying time, it's very easy to work with and is the preferred option for DIYers for coating the first three layers over drywall joints. However, an all-purpose compound is not as strong as other types, such as topping compound.
A specialty form of all-purpose compound is known as lightweight all-purpose mud, which is similar to standard all-purpose mud but is lighter in weight. Some pros find it inferior for taping seams since it contains less binding agent. The lightweight form of all-purpose mud is sometimes used for the first and second coat on seams and for finishing corner bead. It is a very easy mud to sand.
Topping Compound: Best Mud for Final Coats
Topping compound is the ideal mud to use after the first two coats of taping compound have been applied to a taped drywall joint. Topping compound is a low-shrinking compound that goes on smoothly and offers a very strong bond. It is also highly workable. Topping compound typically is sold in dry powder that you mix with water. This does make it less convenient than premixed compound, but it allows you to mix just as much as you need; you can save the rest of the dry powder for future use. Topping compound is sold in pre-mixed boxes or buckets, too, though, so you can purchase whichever type you prefer.
Topping compound is not recommended for embedding joint tape—the first coat on most drywall joints. When applied properly, a topping compound should reduce your sanding time in comparison to lightweight compounds, such as all-purpose mud.
Taping Compound: Best for Applying Tape and Covering Plaster Cracks
True to its name, a taping compound is ideal for embedding joint tape for the first phase of finishing drywall joints. Taping compound dries harder and is more difficult to sand than all-purpose and topping compounds. Taping compound is also the best option if you need to cover plaster cracks and when superior bonding and crack-resistance are required, such as around door and window openings (which tend to crack due to house settling). It is also the best mud option for laminating drywall panels in multi-layer partitions and ceilings.
Quick-Setting Compound: Best When Time Is Critical
Commonly called "hot mud," quick-setting compound is ideal when you need to finish a job quickly or when you want to apply multiple coats on the same day. Sometimes called simply "setting compound," this form is also useful for filling deep cracks and holes in drywall and plaster, where drying time can become an issue. If you are working in an area with high humidity, you might want to use this compound to ensure a proper drywall finish. It sets by chemical reaction, rather than simple evaporation of water, as is the case with other compounds. This means that quick-setting compound will set in damp conditions.
Quick-setting mud comes in a dry powder that must be mixed with water and applied immediately. Be sure to follow the manufacturer's recommendations prior to use. It is available with different setting times, ranging from five minutes to 90 minutes. "Lightweight" formulas are relatively easy to sand.
What Are Dry and Pre-Mixed Joint Compounds?
Drywall joint compound comes in either of two forms: dry or wet. Dry joint compound is the classic type that has been used for years and is still used by professionals. Wet joint compound is a newer product more aimed at the residential do-it-yourselfer.
Both dry and pre-mixed joint compounds contain latex additives to strength and flexibility. When mixed appropriately, both cover the same amount of drywall: about 125 to 150 pounds of compound covering about 1,000 square feet of drywall panels.
Dry Joint Compound
Longer shelf life
Protected against freezing
Difficult to mix
Requires extra tools to mix properly
Joint compound in the dry form is a powder that usually comes in large paper bags. The dry product must be mixed with potable water in a separate container to form workable mud. This product is usually not labeled as being dry. Simply, it will be called joint compound with the qualifiers ready-mixed or pre-mixed omitted.
Pre-Mixed (Wet) Joint Compound
No extra tools needed for mixing
Spoils quickly and develops mold
Must not be frozen
Dries up faster in the bucket
Heavier to carry
More plastic waste
Wet joint compound, called pre-mixed or ready-mixed, is available in plastic buckets. All water necessary has already been added to the joint compound, though it is possible to thin out the consistency with additional water.
Should You Buy an Electric Joint Compound Mixer?
If you do decide to go the dry joint compound route, an electric mixer may help with mixing since the product is heavy and stiff.
It is possible to mix small amounts of dry mud with an electric corded drill and a paddle mixer. But a mud mixer has a strong motor and low torque for turning heavy compounds, even small mixes of concrete. Plus, it saves your drill for what it was made for: drilling.
How much mudding with dry mix would you have to do to justify the purchase of a mud mixer? Since dry joint compound costs virtually the same amount per square foot of coverage as pre-mixed joint compound, purchasing an electric mixer may only make sense financially if you will need to use it often and with huge quantities of dry joint compound: A good 1/2-inch electric drill with a 7 or 8 amp rating will mix a small quantity of mud easily.
For most applications, dry and pre-mixed joint compound are virtually the same, although the pre-mixed option requires less prep work. Common reasons to choose dry mix instead are that it can dry more quickly, is easier to mix and use in very small amounts, offers extra adhesion when using mesh tape, and has an extra-hard set.
Note that skim coating is extremely thin and is considered to be part of a premium level 5 drywall finish, something that few homeowners will ever take on. Since most drywall finishing confines itself to narrow joint strips, you would need to finish around 400 average-sized rooms' joints to justify the cost of the machine.