Sanding plaster stopping well is the difference between a finish that looks professional and one that shows every imperfection under paint. As a general rule, start with 80–120 grit to flatten ridges and high spots, then move to 150–180 grit for your final pass to achieve a smooth, paint-ready surface. The exact grits you need depend on the stopping compound used, how many coats were applied, and the sheen level of your topcoat.
Why Grit Selection Matters
Plaster stopping — whether you're using a lightweight finishing compound or a harder base coat — is relatively soft compared to timber or metal. Using too coarse a grit tears the surface and leaves deep scratches that telegraph through paint, especially with satin or semi-gloss finishes. Going too fine too early just clogs your paper and wastes time. A progressive grit sequence is the key to an efficient, quality result.
The Recommended Grit Sequence
Step 1 — Flatting (80–100 Grit)
Use 80 or 100 grit only where you have obvious ridges, tool marks, or proud stopping that needs knocking back. This is your most aggressive cut, so use it sparingly and with a light touch. A sanding pole with a flat pad helps keep even pressure across the wall and avoids creating hollows. Don't use 80 grit across an entire wall unless the stopping is genuinely uneven.
Step 2 — Intermediate Sanding (120 Grit)
120 grit is a good all-round grit for general flatting of dried stopping coats. It removes the scratches left by 80–100 grit and starts to refine the surface. Many experienced plasterers go straight to 120 grit for most of their sanding work, skipping the coarser grits unless there's a specific problem to address.
Step 3 — Finishing (150–180 Grit)
Finish with 150 or 180 grit to remove the 120-grit scratches and leave a surface fine enough for primer and topcoat. This is especially important if you're painting with a satin, semi-gloss, or gloss finish, which will highlight any remaining scratches. For walls that will be painted with flat or low-sheen paint, 150 grit is usually sufficient.
Quick Reference Table
| Grit | Use | When to Use |
|---|---|---|
| 80 | Coarse flatting | Heavy ridges, proud stopping only |
| 100 | Medium flatting | Moderate unevenness |
| 120 | General sanding | Most stopping coats |
| 150 | Fine finishing | Pre-paint, most sheens |
| 180 | Very fine finishing | High-sheen paints, critical areas |
Wet Sanding vs Dry Sanding
Wet sanding with a damp sponge is a popular alternative, particularly for final coats of lightweight finishing compound. It produces almost no dust, which is a big advantage in occupied homes. The trade-off is that it's easier to over-wet the stopping and cause it to pill or smear. Wet sanding works best on the final, thinnest coat and is not suitable for harder base coat compounds.
Dry sanding with a pole sander and the grit sequence above is the more common approach for most NZ plasterers and is better suited to harder compounds and base coats.
Dust and Health — Don't Skip This
Plaster dust is a real health hazard. Fine silica particles can cause serious lung damage with repeated exposure. WorkSafe NZ classifies respirable crystalline silica (RCS) as a significant workplace hazard. Always wear a P2-rated dust mask (not just a paper dust mask), use dust extraction where possible, and ensure good ventilation. If you're sanding in an occupied home, seal off the work area and protect soft furnishings.
Tips for a Better Result
- Always sand under good lighting — a work light held at a raking angle across the wall reveals imperfections that overhead lighting misses.
- Don't press too hard — let the abrasive do the work. Excess pressure creates hollows and uneven surfaces.
- Change your paper regularly — clogged sandpaper stops cutting cleanly and starts burnishing the surface instead.
- Prime before you assess — apply a coat of Resene or Dulux primer-sealer before your final inspection. Primer reveals remaining imperfections far more clearly than bare stopping.
- GIB board joints need particular care — follow the GIB stopping system recommendations for your specific board type and joint compound.
Choosing the Right Sandpaper
For plaster stopping, aluminium oxide sandpaper is the most common and practical choice — it's widely available at Bunnings and Mitre 10 and suits both hand sanding and pole sanders. Silicon carbide paper is also suitable and tends to stay sharper longer on soft compounds. Avoid cheap no-name paper that sheds grit — it can contaminate your stopping surface.
When to Call a Professional
If you're working on a new build or significant renovation, stopping and finishing plasterboard to a Level 4 or Level 5 finish (as required under the GIB finishing system for high-sheen paints) is a skilled trade. Poor stopping that's been over-sanded or unevenly finished can be very difficult to correct without re-stopping. If you're unsure about the quality of your work, or if you're dealing with a large area, cracked stopping, or a high-specification finish, it's worth bringing in a qualified plasterer. You can find experienced local plasterers on tradedirectory.co.nz.
Note: Stopping and plastering work on walls and ceilings is generally not restricted work under the NZ Building Code, so homeowners can carry out their own stopping. However, if your project requires a building consent, check with your local council about what inspections or documentation may be required.
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