Walk into a Home Depot drywall aisle and you'll see six different buckets of joint compound staring back at you. All-purpose, topping, taping, setting-type 20-minute, 45-minute, 90-minute. Which one do you actually use for skim coating? Here's the pro answer.
The short answer
For skim coating with a wide blade like the PLONIC 32", use pre-mixed all-purpose or topping joint compound, thinned with water to pancake-batter consistency. Skip setting-type ("hot mud") for skim work — it's for filling and patching, not finishing.
The 4 main types of joint compound
1. All-purpose (pre-mixed)
The blue or green lid bucket. This is the most common, most forgiving compound on the market. It's pre-mixed, ready to use, and works for taping, second coats, and skim coating. The drawback is it dries slowly (12–24 hours between coats) and shrinks more than topping compound, so you may see slight cratering over deep fills.
Best for: General-purpose drywall work, contractors who want one bucket that does everything, skim coating residential walls.
2. Topping (pre-mixed)
The white or cream lid bucket. Topping compound is specifically formulated for the final coat. It's lighter, smoother, sands easier, and shrinks less than all-purpose. The trade-off: it's so smooth it has almost no body, so it can’t fill gaps or low spots on its own.
Best for: Final skim coat over a filled and primed wall, Level 5 finish work.
3. Taping compound (pre-mixed)
Heavier bodied than all-purpose. Designed for the first tape coat over seams and corner bead. Too stiff for skim coating — it doesn't spread thin enough and leaves tool marks.
Best for: First coat tape only. Don't skim with this.
4. Setting-type (powder / hot mud)
Comes as a powder you mix with water. Sets by chemical reaction, not evaporation. Very hard when dry, does not sand easily. Available in 20, 45, and 90-minute working times.
Best for: Filling deep voids, patching, bedding mesh tape in repairs. Not for skim coating.
Which compound to use for skim coating
The pros use one of two approaches:
The all-purpose approach (most common)
Grab a 4.5-gallon bucket of all-purpose (USG Sheetrock All Purpose, National Gypsum Gold Bond, or similar). Add water a little at a time — about 1 cup per gallon of compound — and mix with a paddle mixer until it drops slowly off your blade like thick pancake batter. Too thick and you'll leave ridges; too thin and it'll sag.
This is the right move when you're doing residential work, you don't want to buy multiple buckets, and the wall doesn't have major low spots to fill.
The two-bucket approach (Level 5 work)
First coat: slightly thinned all-purpose to fill the texture and build the surface. Second coat: well-thinned topping compound for a glassy, ultra-smooth finish. The topping coat sands to dust — you barely touch it with 120-grit before priming.
This is what you do when the job calls for a true Level 5 finish — hotels, high-end residential, any surface that will be painted with a sheen finish.
How to thin joint compound correctly
Thinning is the most important prep step and the one most new skim coaters skip. Here's the method:
- Open the bucket and scoop out compound into a clean 5-gallon bucket (easier to mix)
- Add clean water slowly — about 8 oz at a time
- Mix with a 650 RPM paddle drill until fully incorporated
- Test by lifting your blade: compound should drip slowly and hold a peak, not run or chunk
- Let it sit 5 minutes, mix again — compound often tightens back up as it sits
Under-thinned compound drags and tears. Over-thinned compound runs down the wall and sags. Take the time to get it right before you load your blade.
Best brands for skim coating
All-purpose
- USG Sheetrock All Purpose — the standard. Available everywhere, consistent batch to batch, blue lid.
- National Gypsum Gold Bond — slightly smoother than USG, preferred by some finishers in the Northeast.
- CGC (Canada) — same formulation as USG, made for the Canadian market.
Topping
- USG Sheetrock Taping/Topping — the cream lid. Fine-grained, easy to sand.
- Beadex FormCoat — popular in production finishing, very smooth finish.
What the pros avoid
- Lightweight all-purpose (purple lid) — too airy for skim coats, doesn't sand cleanly.
- Store-brand compound — inconsistent quality, not worth the $2 savings.
Using the right blade matters as much as the compound
Even the best compound performs poorly with a stiff or worn blade. The PLONIC 32" skimming blade has 0.5mm stainless steel that rides wall undulations and keeps even pressure across the full width — so your compound goes on in a consistent, thin layer every pass. Pair it with well-thinned topping compound and you'll finish walls in two coats that would take three with a stiffer blade.
Quick reference guide
| Product | Use for skim coat? | Notes |
|---|---|---|
| All-purpose (pre-mix) | ✓ Yes | Thin to pancake-batter; most common choice |
| Topping (pre-mix) | ✓ Yes (final coat) | Lightest, smoothest, easiest to sand |
| Taping compound | ✗ No | Too stiff, use for first tape coat only |
| Setting-type (hot mud) | ✗ No | For repairs/fills, not skim finishing |
| Lightweight all-purpose | ⚠️ Avoid | Too airy, poor sanding results |
Bottom line
For most skim coating work: grab a bucket of all-purpose, thin it properly, and use a quality wide blade. For Level 5 finish: two-bucket method with topping compound on the final coat. Either way, do not use setting-type compound for skim coats — it's the most common beginner mistake and it costs you hours of hard sanding.