How do I fill and sand a wall so the repair does not show?
Proud filling, thin coats and sanding beyond the edges — the technique that makes a repair invisible under paint.
- Difficulty
- beginner
- Time
- 1 hr
- Read
- 2 min
Short answer
Fill slightly proud, let it dry completely, then sand back flush feathering well beyond the repair. Most visible repairs are either sunken because the filler shrank, or ringed because the sanding stopped at the edge.
A filled repair shows for one of two reasons: it is not level with the wall, or the transition to the surrounding surface is abrupt. Filling proud fixes the first, feathering the sanding fixes the second.
What you'll need
- Filler
- Filling knife
- Sandpaper
- Sanding block (optional)
- Primer (optional)
Step by step
- Prepare the hole before filling.Scrape away loose material, brush out dust, and undercut the edges slightly so the filler has something to grip.
- Fill slightly proud of the surface.Most fillers shrink as they dry. Filling level means a sunken repair that shows under paint at every angle.
- Use thin coats for deep holes.Anything deeper than about 5mm should be built up in layers, each dried before the next. A single deep fill cracks and shrinks.
- Let it dry completely.Check the packet — usually a couple of hours, longer for deep fills. Sanding damp filler drags and tears.
- Sand with a block, not just your fingers.Fingers follow the contour of the hole and hollow it out. A flat block cuts the proud filler down to the surrounding level.
- Feather the sanding well beyond the repair.Work outwards in decreasing pressure. A hard edge around the repair shows as a ring under paint — this is the step people skip.
- Run your hand over it with eyes closed.Touch detects level changes far better than sight. If you can feel the repair, so will the paint.
- Prime the repair before painting.Filler absorbs paint differently from the wall, so an unprimed repair shows as a dull patch. Spot-prime, or paint the whole wall.
Tips
- Lightweight fillers sand very easily but are weaker. Use a stronger filler for anything that will be knocked or drilled near.
- Check the repair in raking light — a torch held at a shallow angle to the wall shows every imperfection that overhead light hides.
- For a large repair, painting the whole wall rather than spot-touching avoids the patch showing as a slightly different sheen.
Common mistakes
- Filling level with the surface — Filler shrinks as it dries, so the repair ends up sunken and shows as a shadow under paint.
- Sanding only the filler — It leaves a hard edge that shows as a ring. Feather the sanding well out into the surrounding wall.
- Painting without priming the repair — Filler absorbs paint differently, so the repair shows as a dull patch through the finish coat.
Questions people ask
Why can I still see where I filled a hole?
Either the filler shrank and left a hollow, the sanding left a hard edge, or the repair was not primed so it absorbs paint differently. All three are fixable.
How long should filler dry before sanding?
Usually a couple of hours for a shallow fill and considerably longer for a deep one. Check the packet — sanding damp filler drags and tears rather than cutting cleanly.