How to Paint a 3D Print: From Sanding and Primer to a Clean Finish

Prep the Part Before Any Paint Touches It

A clean paint job is mostly decided before you open a can. Pull the supports, clean up any leftover brim, and glue multi-part prints together first. Polymaker's documentation says parts should be fully assembled, sanded smooth and free of debris before priming. Seams and glue joints hide much more easily under primer than after the color goes on.

Layer lines are the main thing between you and a smooth finish. The more visible they are, the more sanding and priming you'll have to do. If you know a part is going to be painted, slice it at a finer layer height. That cuts down on finishing work, though the print takes longer. Start sanding with a medium grit to knock down the ridges, then move to finer grits. Finish with a thorough dust-off. Polymaker recommends compressed air or a strong blower. Formlabs adds a tack cloth, a cotton cloth with a waxy coating that picks up dust and hair. Fold it and use long, gentle strokes in one direction.

Pick a Primer and Spray It Right

Primer is the step you don't skip. According to Polymaker, it's essential for paint adhesion. A filler primer goes further by filling small pits and smoothing the surface. Start with a flat gray. It's neutral, and it shows flaws your eye misses on shiny or colored plastic.

Spray outdoors or in a spray booth, over a drop cloth. Polymaker says to apply a light, even coat from 6 to 12 inches away to avoid drips. Two thin mist coats are better than one heavy coat that buries the details. Per the same source, give the primer at least two hours to cure before you sand or paint. Spray cans release solvents and fine particles into the air. Formlabs recommends a NIOSH-approved respirator, a well-ventilated space and nitrile gloves, which also keep fingerprints off the part. Our ventilation and safety guide covers how to set up your workspace.

Sand the Primer, Then Repeat Until It's Smooth

Once the primer is dry, fine sanding removes the last imperfections. Polymaker suggests something in the 800 to 1200 grit range at this stage. The full loop is prime, sand, clean, repeat. Each pass fills the layer lines a little more until the surface looks close to flawless. Check the part under a low-angle light: any lines that are left show up as shadows.

Don't overdo it, though. Polymaker warns that too much sanding can wipe out fine details like crisp edges, textures and engraved lettering. Sand those areas by hand without a block, or live with a faint trace. For an extra-smooth base, Formlabs uses three-stage nail buffing sticks from the drugstore. Skip the coarsest stage and use only the buff and polish stages. The primed surface ends up slightly glossy. Wipe it with the tack cloth one more time before you add color, because any dust left now gets trapped under the paint.

Build Color in Thin Coats

Deep, even color comes from thin coats. Formlabs explains that a glossy finish means building up thin, even layers. Start and end each pass off the model, move quickly and rotate the part as you go. Before spraying, the company suggests gently swirling the mixing ball in the can for 2 to 3 minutes. Shaking hard can put bubbles in the spray.

Lay down an undercoat first to hide the gray primer: black for darker tones, white for light colors. Per Formlabs, it usually takes 2 to 3 thin coats to cover. The first ones look translucent, which is normal. Once the coat is opaque, let it dry for 20 to 30 minutes. Treat the topcoat like a glaze: the thinner it is, the more the undercoat shows through. Choose a thin paint that's easy to control. Formlabs warns against hardware store paint, which tends to clump into thick, rough layers. Between colors, standard blue painter's tape works well. Press the edges down with something like a credit card, and don't leave the tape on for days.

Airbrush, Brush, and Flexible Filaments

Spray cans and airbrushes give you even coverage and smooth gradients, so they're ideal for large surfaces. Polymaker notes they're less precise on intricate details, though. For eyes, fine lines or textures, switch to a high-quality thin brush. The recommended approach combines both: airbrush for broad coverage, brush for details. That's the standard workflow for cosplay armor and props.

For paint, Polymaker compares two options. Acrylics are affordable and easy to find, but it takes practice to get them on smoothly. Model paints carry more pigment and give more professional results. People often forget about the material underneath. On a flexible filament like TPU, acrylics crack when the part flexes, so Polymaker recommends paints made to stay flexible. In general, match your paint to the filament to avoid cracking and peeling. And be patient: rushing the drying leads to clumps and uneven texture.

Clear Coat and Let It Cure

A clear coat seals and protects the color. Polymaker recommends a satin or gloss spray to finish, and Formlabs notes that matte works too. A clear coat evens out small surface flaws, but it won't fix a poorly primed part. Apply 1 or 2 thin, even coats, just enough for the tiny droplets to flow together into a smooth, even film. To avoid compatibility problems, use a clear from the same paint line or follow the paint maker's recommendation.

For a high-gloss look, Formlabs suggests buffing the paint between coats. On color coats and clear coats, it uses polishing paper, which is finer than regular sandpaper. You can then go over the finished surface with an ultrafine polishing cloth or carnauba wax. Then comes the hardest part: waiting. There's no hard rule, but Formlabs recommends letting the model rest for at least a week so the paint hardens all the way through. If you have to move it sooner, wear gloves and handle it gently.

Sources and limits

• Polymaker Wiki — Painting
• Formlabs — The Ultimate Guide to Painting 3D Printed Parts

We organize manufacturer and community documentation; we have not measured these products ourselves. The manual for your exact model takes precedence over general guidance.