Do you need to prime a 3D print before painting?

Yes, if you want the layer lines gone. Sanding removes the peaks but not the valleys, and paint is too thin to fill them. A sandable filler primer sits in the valleys and gives you a surface to flatten.

What paint works on 3D prints?

Over primer, ordinary acrylic spray or brush paint works on PLA, PETG and ABS alike, because the primer is the surface the paint bonds to. Straight onto bare plastic, acrylics are the safer choice; solvent-based paints can craze ABS.

How do you get rid of layer lines before painting?

Sand with coarse grit to take the peaks down, spray a filler primer to fill the valleys, then sand the primer back. Repeat the primer step if lines still show. Two coats is normal on a visibly ridged print.

Should I wash a 3D print before painting it?

Yes. Skin oil from handling sits in the surface texture and stops paint keying to it. Warm water and dish soap, dried fully, then handle it by an edge.

How to paint a 3D print so the finish lasts

Workshop · Finish

Almost every bad paint job on a 3D print is a preparation problem rather than a paint problem. Sand the layer lines back, wash the part, spray a filler primer to fill what is left, sand that, and only then paint. Primer is the step people skip and the step that decides the result.

Wash the part before you touch it with anything

Handling a printed part puts skin oil into the surface texture, and paint will not key through it. Warm water and dish soap, then dry fully, and handle it by an edge or with gloves afterwards.

This costs two minutes and it is the difference between a finish that survives handling and one that lifts in sheets the first time it is picked up.

Filler primer does the work sanding cannot

Sanding takes the peaks off the layer lines but it will not fill the valleys, and paint is far too thin to bridge them. Filler primer, sometimes sold as high-build or sandable primer, is thick enough to sit in those valleys and give you a surface to flatten.

The sequence that works is sand, prime, sand the primer, prime again if lines still show. Each pass is faster than the one before it because there is less left to remove. On a part with visible layer lines, expect two primer coats.

Primer also gives paint a consistent colour to sit on, which matters more than it sounds. Spraying a light colour straight onto a dark print costs several extra coats and buries detail.

Which paint on which plastic

Once a part is primed, the primer is the surface and the paint no longer has to bond to the plastic at all. That is the point of it, and it is why the same acrylic works over PLA, PETG and ABS alike.

Unprimed is a different question. Acrylics will sit on PLA reasonably well. PETG is a poor host for paint without primer, and ABS is chemically vulnerable to solvent-based paints, which can soften and craze the surface. If you are painting straight onto plastic, test on a scrap piece from the same spool first.

Spray in thin coats and let each flash off. A heavy coat runs, and a run on a textured print cannot be sanded out without going back to bare plastic.

Heat, again

PLA softens at temperatures a dark part reaches in sunlight, and it will certainly soften if a heat gun is used to speed drying. Let paint cure at room temperature.

This is the same constraint that governs sanding PLA. The material is not being awkward, it simply has a low glass transition, and every finishing step has to respect it.

What this needs

Each item is listed with the specification that decides whether a given product will actually do the job, because that is the part product titles tend to leave out.

Filler primer

Sandable and high-build, rated for plastic on the can

Fills the valleys between layer lines that sanding cannot reach. Check the can lists plastic: much filler primer is solvent-based automotive product, and solvent can craze ABS and soften PLA.

Bartoline · Sandable filler primer, greyOne of the few filler primers whose own label names plastic alongside metal and wood

Wet/dry sanding assortment

A grit sequence, not one sheet

Layer lines come off with coarse grit and primer is flattened with fine. Jumping straight to fine paper polishes the peaks and leaves the valleys.

Assorted · Wet/dry sandpaper assortment120 through 3000 grit, wet/dry backing so PLA can be sanded without heat

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Common questions

Do you need to prime a 3D print before painting?: Yes, if you want the layer lines gone. Sanding removes the peaks but not the valleys, and paint is too thin to fill them. A sandable filler primer sits in the valleys and gives you a surface to flatten.
What paint works on 3D prints?: Over primer, ordinary acrylic spray or brush paint works on PLA, PETG and ABS alike, because the primer is the surface the paint bonds to. Straight onto bare plastic, acrylics are the safer choice; solvent-based paints can craze ABS.
How do you get rid of layer lines before painting?: Sand with coarse grit to take the peaks down, spray a filler primer to fill the valleys, then sand the primer back. Repeat the primer step if lines still show. Two coats is normal on a visibly ridged print.
Should I wash a 3D print before painting it?: Yes. Skin oil from handling sits in the surface texture and stops paint keying to it. Warm water and dish soap, dried fully, then handle it by an edge.

Materials this matters most for

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