Two families
Joint compound is either drying-type, which hardens as the water evaporates, or setting-type, which hardens by a chemical reaction after you mix the powder with water. Drying-type is usually sold ready-mixed in pails and boxes. Setting-type is sold as powder in bags, labeled with its working time.
The main types
| Type | Form | Best for | Notes |
|---|---|---|---|
| All-purpose | Ready-mixed | Every coat: taping, filling, finishing, light texture | The simplest choice for small and DIY jobs |
| Taping | Ready-mixed or powder | Embedding tape, first coat | Strong bond, harder to sand |
| Topping | Ready-mixed | Second and third coats | Smooth, easy to sand, weaker bond for tape |
| Lightweight all-purpose | Ready-mixed | Finishing coats and general use | Lighter to carry, sands easily, a little softer |
| Setting-type (hot mud) | Powder | Tape coat, deep fills, patches, gaps, fast schedules | Hardens in a set time; harder to sand |
Setting-type working times
Setting compounds are named by roughly how long you have to work them, such as 5, 20, 45 and 90 minutes. The real time varies with water temperature, room temperature and how clean your tools and bucket are.
| Labeled time | Typical use |
|---|---|
| 5 minutes | Tiny patches; too fast for most jobs |
| 20 minutes | Small repairs, filling holes |
| 45 minutes | Tape coat and filling on a room-sized job |
| 90 minutes | Larger areas and beginners who need more time |
Setting compound does not shrink much and keeps hardening even in cold, damp rooms, so it is good for the first coat and deep fills. Because it gets hard, many finishers top it with a ready-mixed compound that sands easily.
Ready-mixed or powder?
| Ready-mixed (drying-type) | Powder (setting-type) | |
|---|---|---|
| Preparation | Open and stir; can be thinned slightly | Mix with clean water each time |
| How it hardens | Water evaporates, usually overnight | Chemical set in the labeled time |
| Shrinkage | More; deep fills may need extra coats | Less |
| Sanding | Easier | Harder |
| Cold or damp rooms | Dries slowly | Sets on schedule |
| Shelf life once opened | Good if sealed and kept from freezing | Dry powder keeps if stored dry; mixed batches cannot be saved |
A common system
- Tape coat: all-purpose or taping compound, or a setting-type powder. Embed paper tape firmly with no air bubbles.
- Second coat: all-purpose or topping, feathered wider than the tape.
- Third coat: topping or lightweight, feathered wider again, then sanded smooth.
Screw heads and corner bead get three coats too. For a small job, one pail of all-purpose for everything is fine.
Paper tape or mesh tape?
Paper tape works with any compound, is stronger at joints and is standard for inside corners. Self-adhesive mesh tape is quick to apply, but it is usually paired with setting-type compound for the first coat, because ready-mixed compound over mesh is more likely to crack along the joint.
Worked example: how much to buy
For a standard finish, a common rule of thumb is about 9.4 gallons of ready-mixed compound and 370 ft of tape per 1,000 sq ft of drywall. A 12 × 14 ft bedroom with 8 ft walls, hung with fifteen 4 × 12 ft sheets on the walls and ceiling, has 720 sq ft of drywall. With 10 percent extra that is about 7.4 gallons, two 4.5 gallon pails, and about 293 ft of tape, two 250 ft rolls or one 500 ft roll. If you use setting powder for the tape coat, buy a little less ready-mixed compound and a bag of powder. Run your own area or sheet count through the joint compound calculator.
Tools that make it easier
- A 6 in taping knife for the tape coat and screws, and a 10 or 12 in knife for the wider finish coats.
- A mud pan or hawk to hold a working amount of compound and keep the pail clean.
- An inside-corner tool for corners, which saves time if you have many of them.
- A drill-mounted paddle mixer for powder and for loosening ready-mixed compound.
- A sanding pole or sponge, and a bright work light held low against the wall to show ridges before you paint.
Clean knives and pans as you go. Dried bits of compound in the next coat leave scratches and pits.
Storage and safety
- Keep ready-mixed compound from freezing, and press plastic onto the surface before sealing the lid to stop a skin forming.
- Never return leftover mixed setting compound to the bag or mix it with ready-mixed compound; it will set.
- Do not pour setting compound down a drain; it can harden in the pipes.
- Sanding dust is fine and gets everywhere. Use dust-controlled sanders or wet sponging, a fitted respirator, and seal off the room.
Frequently asked questions
Can I use all-purpose joint compound for everything?
Yes. All-purpose ready-mixed compound works for taping, filling and finishing coats, which is why it is the usual choice for small jobs.
What is hot mud?
Setting-type joint compound sold as powder. It hardens by chemical reaction in a labeled working time, such as 20, 45 or 90 minutes, instead of by drying.
How much joint compound do I need for one room?
A 12 × 14 ft bedroom hung with fifteen 4 × 12 ft sheets has 720 sq ft of drywall. That takes about 7.4 gallons with 10 percent extra, two 4.5 gallon pails, plus about 293 ft of paper tape.
Do the math for your own project.
Open the joint compound calculator