7 minute read -
Sanding Plaster: Choosing the Right Sander and Grit
For sanding plaster, a long-reach wall sander with dust extraction works best on large areas, and sanding mesh on a hand block is ideal for small patches and corners. Start with 80 or 100 grit for nibs and ridges, and finish with 120 to 150 grit.
Always connect a vacuum extractor or wear at least an FFP2 dust mask, because plaster dust is extremely fine.
What will you learn in this article?
- When should you sand plaster?
- Should you sand plaster by hand or with a machine?
- Which sander is suitable for plaster?
- Which grit of sanding mesh should you use for plaster?
- How to sand plaster step by step
- How do you keep the dust under control?
- Sanding safely: take care with old ceilings and walls
- Common mistakes when sanding plaster
- Frequently asked questions about sanding plaster
- In short: sanding plaster
When should you sand plaster?
New plaster is rarely perfectly smooth. There are trowel marks, small nibs, dried splashes and ridges at corners and along the ceiling line. You only really see them once a coat of emulsion is on, and by then it is too late. That is why you sand before painting or wallpapering.
Only sand once the plaster is completely dry. Fresh plaster is dark and feels cool to the touch. When the colour is light and even all over, it is usually dry. How long that takes depends on the thickness, the temperature and the ventilation. Allow several weeks for a normal coat of plaster and keep the room well ventilated in the meantime.
Should you sand plaster by hand or with a machine?
For a small area, such as a filled hole or a strip next to a window frame, sanding by hand is fine. Use sanding mesh on a sanding block with clamps. Mesh clogs less quickly than ordinary sandpaper, because the dust falls through the openings.
For a whole wall or ceiling, a machine is faster and gives a more even result. By hand you tend to press harder in some places without noticing, which sands dips into the plaster. A machine spreads the pressure better over a large sanding surface.
| Method | Suitable for | Watch out for |
|---|---|---|
| Sanding mesh on a hand block | Repairs, corners, small areas | Press lightly and keep changing direction |
| Long-reach wall sander (giraffe sander) | Whole walls and ceilings | Always use dust extraction |
| Random orbit sander | Smaller walls, edges, transitions | Avoid coarse mesh, it quickly sands too deep |
| Detail sander | Internal corners and awkward spots | Small sanding pad, so not for large areas |
Which sander is suitable for plaster?
Long-reach wall sander for large areas
A long-reach wall sander has a round sanding head on a long pole. It lets you reach the top of a wall and much of the ceiling without scaffolding. The head pivots with the wall so you keep sanding flat. Choose a model with a connection for a vacuum or dust extractor and variable speed. On plaster you usually work at a low to medium speed so you do not go through the top layer.
Random orbit sander for smaller walls
If you only have one wall or a few repairs, a random orbit sander also works. It is lighter and easier to handle. Use fine mesh or sanding discs for plaster and keep the sander flat against the wall. If you tilt it, the edge grinds a ring into the plaster. A cordless sander, for example from the Batavia Maxxpack 18V range, is handy when you are working on a stepladder without a cable. Check the manual to see which sanding discs and dust extraction options suit your sander.
Sanding a ceiling without a long-reach sander
Without a long-reach wall sander, sand a ceiling from a stable platform or scaffold tower using a hand block or a light random orbit sander. Work in strips about a metre wide and take regular breaks. Sanding overhead is hard work, and tired arms lead to uneven results.
Which grit of sanding mesh should you use for plaster?
Plaster is soft, so you do not need a coarse grit.
- 80 to 100 grit: to remove nibs, splashes and ridges in the plaster.
- 120 grit: the standard grit for levelling a whole wall.
- 150 to 180 grit: for finishing when the wall will get a smooth eggshell or a thin coat of emulsion.
You almost never need anything coarser than 60 grit on plaster. It is more likely to leave scratches and dips than to make the surface flat.
How to sand plaster step by step
Protect the room
Empty the room or cover furniture and floors with protective sheeting and dust sheets. Tape over sockets and switches.
Contain the dust
Open the windows and seal the doors to the rest of the house with plastic sheeting.
Connect extraction and protect yourself
Connect the vacuum to the sander and put on an FFP2 or FFP3 dust mask and safety goggles.
Tackle the nibs and ridges
Start with 100 grit on the nibs and transitions. Use light pressure and work in overlapping circles or strips.
Check with raking light
Shine a lamp at a low angle across the wall. Raking light shows up bumps you miss when looking straight on.
Go over the whole wall
Sand the whole wall again with 120 grit.
Remove the dust
Vacuum the wall or brush it down with a clean, dry brush.
Prime before painting
Apply a primer or mist coat before painting, so the emulsion bonds well and is not absorbed too quickly.
How do you keep the dust under control?
Plaster dust is so fine that it gets through gaps into every part of the house. Extraction at the source works best: a long-reach wall sander connected to a dust extractor prevents most of the dust cloud. An ordinary household vacuum clogs quickly with fine dust, while a dust extractor with a suitable filter keeps going for longer.
Always wear respiratory protection as well. A simple face covering does not stop plaster dust, but an FFP2 mask does. Wash your work clothes separately and vacuum the room thoroughly after sanding, before you start painting.
Sanding safely: take care with old ceilings and walls
Never sand an old textured ceiling, an Artex-type coating or old decorative plaster yourself if you do not know what is in it. In the UK, asbestos was banned in 1999, so textured coatings in buildings built or refurbished before 2000 may contain it. Sanding releases the fibres. Have it tested first, and if the result is positive, have it removed by a licensed specialist.
Also switch off or unplug the sander, or take out the battery, when you change the sanding mesh, and always set up a ladder or platform on a flat, non-slip surface.
Common mistakes when sanding plaster
- Sanding too early, while the plaster is still damp. The mesh clogs and you pull out lumps.
- Using mesh that is too coarse, leaving scratches and dips in the wall.
- Pressing too hard with the sander. Let the weight of the sanding head do the work.
- Working without raking light, so you miss uneven spots.
- Leaving the dust on the wall after sanding. Emulsion then bonds poorly and you get bits in the paint.
Frequently asked questions about sanding plaster
Can you sand plaster with an ordinary sander?
Yes. For small areas a random orbit sander with fine mesh works well. Keep the sander flat and do not press too hard. For whole walls and ceilings, a long-reach wall sander with a long pole is more practical.
Which grit should you use on plaster before painting?
Start with 80 to 100 grit on nibs and ridges, then sand the whole wall with 120 grit. For a very smooth finish, you can finish with 150 to 180 grit.
Is sanding mesh better than sandpaper for plaster?
For plaster, yes. Sanding mesh has an open weave, so the dust falls through and the mesh does not clog quickly. Sandpaper soon fills up with plaster dust and needs changing often.
Do you always need to sand plaster?
Not always. A smooth skim finished ready for painting often only needs a light sand on ridges and splashes. Check the wall with raking light and only sand where it is needed.
In short: sanding plaster
Use a long-reach wall sander with extraction for large walls and ceilings, and sanding mesh on a hand block or a random orbit sander for small areas. Sand nibs with 80 to 100 grit and finish with 120 to 150. Always wear a dust mask, and have old textured ceilings tested for asbestos before you touch them.