# Understanding Drywall Joint Compounds: Hot Mud, All‑Purpose, Topping and More

Selecting the right joint compound is essential for efficient drywall finishing. Professionals often refer to “hot mud,” taping compound and topping compound, but what do these terms mean? This blog explores the different types of joint compounds, their advantages, and when to use each.

## Categories of Joint Compounds

Joint compounds are typically categorized into two broad groups: **setting‑type** (often called **hot mud**) and **drying‑type** compounds. Within these groups are products formulated for specific tasks such as taping, all‑purpose use or finishing.

### Setting‑Type Compounds (Hot Mud)

- **Description and chemistry** – Setting‑type compounds are supplied as a dry powder that is mixed with water. Unlike pre‑mixed compounds, they cure by a chemical reaction rather than by evaporation. Because the hardening process is triggered once water is added, these products are colloquially called **hot mud**. Trim‑Tex explains that hot mud is available in different setting times—commonly 20, 45, 90 or 120 minutes—and is ideal for filling deep voids or for quick repairs when you need to apply multiple coats in a single day【410098332597325†L44-L76】. Master Building Materials notes that popular brands include Sheetrock 20, Sheetrock 45 and Sheetrock 90, which set within 20, 45 or 90 minutes respectively【142880795562578†L480-L546】.

- **Advantages** – Hot mud sets fast and shrinks less than drying compounds, allowing you to apply multiple coats in one day or continue work even in cold or humid conditions. It provides strong initial bonding and is useful for embedding tape over cracks or filling large gaps.

- **Considerations** – Because setting‑type compounds harden quickly, they have a limited working time. Mix only what you can use before the product sets and clean tools immediately after use. Some formulas are harder to sand than drying compounds.

### All‑Purpose Compound

- **Versatility** – All‑purpose compound is a pre‑mixed, ready‑to‑use drying‑type compound that can be used for taping, filling and finishing joints. Trim‑Tex lists it as the “jack of all trades” compound【410098332597325†L44-L76】. It contains vinyl binders and limestone, giving it good adhesion and durability. Professionals often use all‑purpose for the first coat over joint tape and for corner beads.

- **Pros and cons** – Because it is pre‑mixed, all‑purpose compound saves time on mixing. However, Master Building Materials notes that some contractors find pre‑mixed all‑purpose to be weaker than dry compounds, particularly when embedding tape【142880795562578†L480-L546】. It can also shrink more during drying, requiring additional sanding.

### Lightweight Compound

- **Reduced weight and easier sanding** – Lightweight compound is a version of all‑purpose compound with lightweight fillers. It is easier to handle and sand, making it a favorite for the second and third coats. It is still a drying‑type compound and typically comes pre‑mixed.【410098332597325†L44-L76】

### Taping Compound

- **Designed for embedding tape** – Taping compound (also known as tapers’ mud) is formulated to be stronger and harder than all‑purpose compound. It is usually supplied as a drying‑type product and is used for the initial coat over joint tape or to cover cracks. Master Building Materials points out that taping compound hardens fast and provides a strong base for subsequent coats【142880795562578†L480-L546】.

### Topping Compound

- **For final coats** – Topping compound is a fine‑grained, smooth drying compound designed for the final coat. It sands easily and produces a smooth surface ready for priming. Trim‑Tex notes that topping compound is not meant for embedding joint tape or corner beads; it should only be used over other coats【410098332597325†L44-L76】.

## Dry vs. Pre‑Mixed Compounds

Master Building Materials contrasts **dry (setting‑type) compounds** and **pre‑mixed compounds**:

- **Dry compound** (powder) allows custom mixing to the desired consistency and offers better adhesion and storage life. Contractors prefer it because it can be stored indefinitely in powder form and mixed on site【142880795562578†L551-L574】. Setting‑type (hot mud) falls into this category.

- **Pre‑mixed compound** comes ready to use but may spoil if stored for long periods once opened. It is convenient for small projects and does not require measuring water【142880795562578†L551-L574】. All‑purpose, lightweight, taping and topping compounds are typically pre‑mixed.

## Working With Hot Mud and Other Compounds

1. **Mixing setting‑type (hot mud)** – Add water gradually to the powder and mix to achieve a peanut‑butter‑like consistency. Use clean tools and only mix the amount you can apply within the working time indicated on the package.

2. **Applying tape** – Use taping or all‑purpose compound for embedding paper or fiberglass tape in joints. Spread a thin, even bed of compound, press the tape into the mud, then immediately cover with a thin layer of compound.

3. **Building up layers** – Once the first coat is dry or set, apply subsequent coats with lightweight or all‑purpose compound. A final coat of topping compound creates a smooth surface for priming.

4. **Sanding** – Use fine‑grit sandpaper (120 or 150 grit) and a light touch. Setting‑type compounds can be harder to sand than drying compounds; in some cases, a damp sponge can smooth ridges without producing dust.

## Summary

Choosing the right joint compound is essential for quality drywall finishing. **Setting‑type compounds (“hot mud”)** cure through a chemical reaction and allow rapid layering for repairs or time‑sensitive projects【410098332597325†L44-L76】. **All‑purpose** and **lightweight** compounds offer versatility but may shrink more. **Taping compound** provides strength for embedding tape, and **topping compound** yields a smooth final coat【142880795562578†L480-L546】. By understanding these options, you can select the best compound for each stage of your project.