Sanding marks showing through paint
The surface felt smooth, but the paint shows every scratch. Paint magnifies sanding marks, so they need to be gone before color.
Quick answer
Sanding scratches show through paint when the last grit was too coarse, scratches were skipped in the grit sequence, or primer was too thin to fill them. Fix by sanding the scratched area back through finer grits (for example, #400 to #800 to #1200 or finer), wiping off dust, then re-priming and checking under angled light before color. Gloss and metallic paints show scratches most.
- TimeRescue: 30-60 minutes plus repriming. Prevention: sanding in sequence.
- DifficultyIntermediate
Safety first
- Wear a dust mask when dry sanding; plastic and resin dust is irritating.
- Wet sanding reduces dust.
- Keep sanding dust away from food and children.
Is this your problem?
- Straight fine lines in the paint where you sandedSanding scratches: this page.
- A pitted or rough texture all overSee Primer grainy or fuzzy.
- A white line or whitened band at a cut or sanded edgeSee White stress marks and nub marks.
- A ridge or line along a joint where you filledSee Seams that keep coming back.
- Mold lines show along the edgeSee Mold lines on miniatures and parts.
You'll see
Fine parallel lines or a hazy texture appear on a surface that looked fine before painting, often visible only under the right light. They can also appear after a gloss coat, when the shine makes every scratch visible.
Likely causes
- Last grit too coarseScratches from coarse sandpaper are deeper than thin paint layers can hide.
- Skipped gritsJumping from a coarse to a fine grit leaves the coarse scratches behind, because the fine grit is too gentle to remove them.
- Thin primerA thin coat of primer does not fill scratches. Surfacer primer is designed to fill light marks.
- Gloss or metallic finishShiny finishes reflect light directly and reveal defects that matte paint would hide.
- Sanding dust left on the partDust trapped under paint appears as bumps or rough texture.
What you need
- Sanding sponges or sticks in graded grits, for example #400 up to #1500 or finer
- Surfacer primer
- Soft brush or air blower for dust
- Good raking light (a flashlight at a low angle)
- Water for wet sanding and a cloth
How to fix it
- Check the scratches in raking light before repainting so you know where they are.
- If paint has not cured, wait. If it is cured, lightly sand the area back to primer or plastic, depending on how deep the scratches are.
- Start with the grit that removes the deepest scratch, then step through finer grits (for example #400, #800, #1200 and up). Do not skip more than one step.
- Sand in one direction, then change direction with each finer grit so you can see when the old scratches are gone.
- Clean off dust with a soft brush or air blower and wipe with a lint-free cloth.
- Apply a thin coat of surfacer primer, which is designed to fill faint tool marks, and let it cure as the maker says.
- Inspect under angled light. Re-sand and re-prime where scratches still show. Only then repaint.
What to avoid
- Painting before checking the surface.
- Jumping from very coarse to very fine grit.
- Using gloss paint as a first test.
Common wrong fixes
- Adding more paint to cover scratches; it magnifies them.
- Sanding the paint without removing the scratch beneath it.
Not worth fixing, or time to ask us
If you are unsure what grit sequence suits your material or paint, ask us before sanding. We can suggest a safe sequence for your case.
By situation or hobby
Plastic with seams
Sand gently and check often; over-sanding can remove detail around the seam.
Resin kits
Wet-sand to avoid dust; resin dust is irritating.
Metal or gloss finishes
Sand finer and prime in gray or white to check surface quality.
Curved parts
Use sanding sponges that follow curves, not hard sticks that make flat spots.
Already ruined?
Light scratches can be sanded out and repainted. Deep scratches in thin plastic may remain visible even after repair if too much material would be removed. If detail has been sanded away, rebuild it with putty or plastic card. Tough cases may need stripping the paint and starting again.
Next time
- Sand through a sequence of grits.
- Finish at a fine enough grit for your paint type.
- Use surfacer primer and inspect before color.
- Remove all dust before painting.
- Check under raking light.
Frequently asked questions
What grit sandpaper should I use on plastic models?
A common sequence is roughly 400 for shaping, 800-1000 for smoothing and 1200 or finer before primer; adapt to the job.
Why do I see scratches after painting?
Paint is thin and does not hide scratches. Gloss and metallic paints make them show more.
How do I fix sanding scratches in paint?
Sand them out in finer grits, clean, apply surfacer primer, inspect, then repaint.
Does primer fill sanding scratches?
Surfacer primers fill light marks; regular thin primers mainly show them.
Should I wet sand?
Wet sanding reduces dust and clogging, and is common for fine grits. Follow the abrasive's instructions.
Jargon explained
- Grit
- A number for the coarseness of sandpaper; higher is finer.
- Surfacer
- A primer designed to fill fine scratches and level a surface.
Tools that can help
-
Stedi 10pcs/box #400~15000 3mm Sanding Sponges from $10.95
Why it helps: Flexible sanding sponges from coarse to very fine grits that conform to curved surfaces.
How to use it
Work through grits on curved areas to remove each scratch in turn.
-
Hobby Mio HMD Double-Sided Sanding Sticks from $10.95
Why it helps: Sanding sticks with two grits per stick, in hard, soft and pointed types.
How to use it
Step from a coarser to a finer grit without changing tools.
-
Guazi Studio 100ml Model Primer Surfacer $23.95
Why it helps: A surfacer primer described as filling faint tool marks and giving an even base; it is meant to be sanded smooth before color.
How to use it
Prime and inspect the surface before applying color, following the maker's instructions.
Reviewed November 3, 2026