How to Sand a Wall Properly Before You Paint
Why sanding is the part that decides how the paint looks
Some painted walls just read better, and it is almost never the paint doing that. It is what happened before the paint went near them. Sanding is the least interesting hour of any painting job and it is the hour that sets the result, because paint does not hide a rough surface, it follows one.
What sanding actually buys you
- Adhesion. Paint grips a keyed, dull surface. It sits on top of a glossy one and peels off later.
- A finish that lasts. A smooth surface is far less likely to chip or blister down the track.
- The look. Lumps and ridges catch the light sideways, which is why a wall can be freshly painted and still look tired.
The mistakes worth avoiding
- Skipping grits. Jumping from coarse straight to fine leaves scratches the fine paper never removes.
- Worn paper. Once the grit is loaded up it polishes instead of cutting, and you work twice as hard for nothing.
- Circles on timber. Swirl marks show up under a topcoat, especially under gloss.
- Not dusting off. Paint hates dust, so wipe down before you open the tin.
Which grit for which job
- 40 to 60 grit. Stripping old coatings or taking out real surface damage.
- 80 to 120 grit. Smoothing timber and keying a wall before primer.
- 150 to 180 grit. Between coats of primer and paint.
- 220 grit and finer. Final passes, between topcoats, and anywhere delicate like cabinetry.
When you are not sure, start finer than you think and only step coarser if it is not cutting. You can always take more off, and you cannot put it back.
By hand or with a sander
Hand sanding wins on light prep, on small or shaped work like frames and sashes, and on the final pass where you want to feel what you are doing. A power sander earns its keep on large flat areas, on serious roughness, and on old paint that has to come off quickly. Either way, let the tool do the cutting rather than leaning on it, because pressure just clogs the paper and burns the surface.
The order of work
- Clean first. Sanding a dirty surface grinds the dirt in.
- Start at a medium grit unless there is old coating to strip.
- Keep the pressure even and let your wrist do the moving.
- Follow the grain on timber. Across it leaves scratches you will see forever.
- Finish at a fine grit.
- Wipe everything down, including the edges and the nooks.
How to tell when it is done
Your fingertips are better at this than your eyes are. Run a flat hand slowly over the surface with your eyes shut. It should feel like clean paper, not gritty and not catching. If your fingers skip or snag anywhere, that spot gets another pass with the fine paper.
Shop related products
- Uni-Pro Aluminium Oxide Sandpaper Roll, 80 Grit. The medium cut for keying walls and timber.
- Uni-Pro Aluminium Oxide Sandpaper Roll, 180 Grit. For between coats.
- Medium Sanding Block, 98 x 69 x 26mm. Keeps the paper flat so you do not dish the surface.
- Supercraft Multi Tool Sanding Sheets, 93mm Assorted, 12 pack. For corners and detail work.
More in paint and accessories, and if you want the paint matched to the prep, our Haymes paint mixing page has the detail.
Read next
- How to sand timber properly, grits, grain and technique
- How to prep your painting tools before you start
Take your time on the prep and the painting bit is the easy part, which is not how it feels at the time.
Cheers,
Candeece
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