Sanding and Painting 3D Prints: A Complete Guide

Jackson B.

The Finishing Touch

The raw output of an FDM printer is impressive in its own right, but for display-quality results, the print is often just the starting point. A properly finished 3D print — sanded, primed, and painted — can be virtually indistinguishable from an injection-moulded product. The finishing process requires patience and attention to detail, but none of the individual steps are technically difficult. This guide walks through the complete workflow from raw print to display-ready finish.

The most important mindset shift for new makers: don't try to rush the finishing process. Every step needs to cure or dry completely before moving to the next. Sanding over un-cured primer ruins the primer. Painting over incompletely dried primer causes lifting and peeling. The total active work time might be 2–3 hours, but the wall-clock time of the full process is often 1–2 days. Plan accordingly.

Sanding: From Coarse to Fine

Start with 120-grit sandpaper to knock off the major surface ridges — the high points of each layer line. Work in smooth, circular motions with consistent pressure. Don't focus on one spot too long — the friction heat can soften PLA and cause it to ball up. Work wet from 220-grit upwards: wet sanding (using water or a small amount of dish soap in water) dramatically reduces dust, prevents clogging the paper, and gives a finer scratch pattern. Progress through 220, 400, 800, 1200, and optionally 2000-grit for ultra-smooth surfaces.

Wet sanding is messy but the results justify it. Work over a tray or outside, rinse the part regularly to see your progress. Between grits, wipe the surface dry and inspect it under a bright, raking light — scratches from the previous grit should be completely replaced by finer scratches before you move up. If you jump from 220 to 800, the deep scratches from 220 won't be removed by 800 — progress is step-by-step.

Priming: The Non-Negotiable Step

Even after thorough sanding, microscopic scratches and tiny surface pits remain. Filler primer (available as a spray can from Bunnings, Repco, or Supercheap) fills these imperfections and provides a uniform base for paint adhesion. Apply two or three thin coats from 30cm distance, allowing 10–15 minutes between coats. Never apply one thick coat — it runs and fills detail.

After the primer cures (typically overnight for a complete cure), sand lightly at 400-grit. The primer will come off the high spots (showing bare plastic) and fill the low spots. This is called "guide-coat" technique — the differential reveals exactly where more work is needed. Apply another coat of primer to the low spots, let cure, sand again. Repeat until the surface is perfectly uniform when sanded at 400-grit. This process is tedious but is the foundation of a professional finish. Consider using matte PLA as your base material — its surface requires less prep work than standard shiny PLA.

Painting: Thin Coats Win Every Time

Regardless of application method — spray can, airbrush, or hand brush — multiple thin coats always beat one thick coat. Thin coats dry faster, don't run, don't obscure fine detail, and build up to a consistent, even colour without texture issues. For spray painting, 25–30cm distance, even passes that start and end beyond the part, is the standard technique. For hand brushing, thin acrylic paint to a slightly watery consistency and apply in smooth strokes, building colour in 2–3 coats.

Finish with a clear coat appropriate to your desired final finish: matte clear for realistic organic surfaces, satin for a balanced look, or gloss for a polished product feel. Automotive clear coats (Rustoleum, Krylon) are excellent over spray-painted bases. Artist's acrylic varnish works over hand-painted acrylics. The clear coat both protects the paint layer and unifies the surface finish. If you'd rather skip all of this, silk PLA produces a striking metallic finish straight from the printer — read our silk PLA guide to see if it suits your project.