Field note
Fast Drying Joint Compound, Choosing the Right Drywall Mud
If you’re planning a drywall project, chances are you’ve had to do some research on fast drying joint compound. While you may understand what drywall mud does, you might not understand why there are so many choices.
Not only that, but what’s the difference is between the products. Let’s clarify what each joint compound is and when to use them.
What is Joint Compound
Joint compound, sometimes referred to as drywall mud or sheetrock mud, is used to cover joints. It’s a gypsum-based mix that connects drywall seams and corner beads, provides extra structure and covers up problem spots for smooth surfaces that are ready for paint.
Some professionals may refer to joint compound broadly as Durabond. This is just a specific brand owned by USG, the folks who make Sheetrock.
Applying Joint Compound and Drywall Tape
Before we dive into the different types of drywall mud, it’s important to cover drywall tape and the process of taping and mudding drywall.
Joint compound and tape are used on the latter end of the drywalling process. After drywall has been measured, cut, and fastened to the walls, the seams and screwheads are covered with layers of joint compound and tape to create a smooth and sturdy finish.
The Three Coat Process
The process works by applying the first coat of compound, allowing dry time to harden. The joints and corners are covered with corner bead and joint tape dried into the mud.
After the first coat dries, a second coat is applied, followed by a third and final coat. After that, it all gets sanded down for a smooth finish. Each coat has a different purpose, the earlier ones focused on structure and adhesion, the latter on a smooth finish.
Therefore, the different types of joint compound can be used at other points of the mudding and taping process.
Difference Between Joint Compound and Plaster
Joint compound has been the preferred method of finishing drywall since the early 20th century. The main difference between drywall mud and the plaster of paris products typical in buildings built before the early 1900s is the hardening effects of plaster.
Drywall mud, or hydrated calcium sulfate, forms when the dry powders of drywall mud mix with water. It’s similar to plaster but lacks the cement-like hardening in the lime and aggregate plaster mix.
Type of Joint Compound
Joint compounds can be broken down into two main categories:
- Fast Drying (AKA Quick Setting or “Hot” mud)
- Premixed drywall mud
You can find dozens of different drywall mud in stores with specific uses and branding.
Quick Setting Drywall Mud
Also called hot mud or fast drying mud, this joint compound is sold in plastic-lined boxes or paper bags in powder form. The gypsum dust is mixed with water, which starts turning the mud from wet to dry.
There are a few rationales as to why this stuff has been called “hot mud.” The actual chemical reaction that begins once you mix the powder with a little water releases a small amount of heat.
Another is that once you mix water into the product, you have to move quickly, or else it’ll set before you fully apply it. Either way, it’s important only to mix as much as you need and use it before it sets.
Additional Coats in Less Time
Fast drying joint compound is sold according to drying times which can vary by manufacturer from 90 minutes to 20 minutes. The quicker setting times of hot mud allow you to apply additional coats in less time, even the same day, along with patching or drywall repairs of troublesome spots where drying might otherwise be an issue.
Many professionals think that hot mud provides a crack-resistant, strong base coat. The downside is that the quick setting stuff is rarely used as a finish coat since it’s difficult to sand for a smooth finish.
One issue professional tapers and finishers understand is that all joint compound shrinks. The amount of shrinkage depends on what type of mud you are applying and a variety of site-specific factors.
USG 20 Minute Easy Sand Joint Compound
Lightweight for easy handling, low shrinkage, and superior bond. Great for small patching and laminating drywall. It’s recommended to use mesh tape on joints where quick-setting compound is used.
Pre-Mixed Drywall Compound
The premixed regular joint compound is great for convenience’s sake since it’s most commonly sold in 5 gallon buckets. It’s typically thinned a little with water before applying, but this is what most people think of when they think of joint compound.
The trade-off for convenience is that the premixed mud has a longer drying time and can be more expensive. The most common types of premixed compound are All-Purpose, All-Purpose Lightweight, and Topping.
All-Purpose Drywall Compound
This mud is named aptly because it really can be used for all purposes. It’s easy to work with and can be used for first coats, embedding tape, small patches, filling nail holes, etc.
The ease of use and universal application make this a favorite for DIYers. However, this regular mud is harder to finish and sand than some others.
All-Purpose Lightweight Drywall Mud
As the name suggests, this joint compound is a lighter weight version of the all-purpose. Some professionals think the lightweight nature means the compound has less binding power and structure than other kinds.
While it’s hard to pin down the truth of that, the lightweight mud can be a better choice as a finishing coat since it’s easier to sand.
Topping Compound
Topping compound is probably the least used of all the drywall muds on this list. However, it makes for a good finishing coat and is often used for texture applications and skim coating.
This stuff is the whitest of all on the list and has less shrinkage in the drying process than the others.
READ more about common drywall partition types,
When to Use Fast Drying Joint Compound
As mentioned above, the setting and drying times of joint compound are probably the most significant factors to consider when choosing whether to use fast drying or pre-mixed.
The pre-mixed compound is convenient and can be used for multiple coats, but the process may take multiple days. Hot mud can expedite the whole process but requires a quick application and taping.
Note that for all types of joint compound, setting and drying times can vary according to the environment. Humid environments can delay drying times significantly, as can cold temperatures.
Dry Times Dependent on Jobsite Enviornment
When using pre-mixed compound, you can speed up the drying process by applying thinner instead of thicker coats. Also, the use of space heaters, hair dryer, or heat gun pointed at the freshly applied mud will speed up dry times.
Often, it comes down to personal preference as to how much time is available to finish the project. A project requiring faster drying is usually on a strict schedule for painters to start as soon as possible.
Industry veterans will be all-to-familiar with the request for painters to start before the taping is allocated proper drying times.
Fast Drying Drywall Compound, Choose Wisely
Use fast drying compound for quick applications, small areas, problem patches, small holes, and sturdy first coats. Use all-purpose pre-mixed versions for larger jobs or a large area, and second and finish coats, generally.
When it comes to mixing and matching joint compounds, follow manufacturer instructions. Most drywall mud is compatible with each other, but it’s best practice to check the manufacturer’s recommendations for compatibility.
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