Post-Processing FDM Prints — Sanding, Priming, and Painting

Off the printer, FDM parts have visible layer lines. Here's how to get a smooth, painted finish worthy of a display or product.

Sanding

Work through grits progressively — don't skip steps.

Tips:

• Wet sand from 400 grit up — less dust, better finish
• PLA sands easier than PETG
• Don't over-sand thin walls — can cut through
• Use a sanding block for flat surfaces to avoid rounding edges

Filling

For deep layer lines or imperfections, fill before priming:

• Spot putty / body filler — works well, sand smooth when dry
• XTC-3D epoxy coating — brush on, self-levels, adds strength
• Polyester primer (high-build) — multiple coats fill shallow lines

Priming

1. Clean part with IPA — remove all oils and dust
2. Apply filler primer in light coats (2–3)
3. Let dry fully (30 min between coats)
4. Sand with 800 grit wet
5. Inspect — re-prime any remaining lines
6. Final 1000–1500 grit before paint

Painting

• Rattle cans work fine for most hobby use
• Adhesion promoter first for PETG/ABS — paint flakes off otherwise
• Light thin coats — 2–3 coats minimum
• Let cure 24 hours before handling

Clear Coat

• Matte, satin, or gloss to taste
• 2K rattle can (2-component) for durability
• Wax after full cure for protection