Post-Processing 3D Prints: Sanding, Painting, and Finishing Techniques

Fresh off the printer, most 3D prints show visible layer lines and rough surfaces. Post-processing transforms these raw prints into polished, professional-looking pieces. Whether you want a smooth painted finish or a natural wood-like texture, this guide covers the essential techniques.

Step 1: Support Removal and Cleanup

Before any finishing work, remove all supports and clean up the print:

• Use flush cutters or needle-nose pliers to remove support structures.
• A craft knife or scalpel is ideal for cleaning up support attachment points.
• Sand away any remaining nubs with 120-grit sandpaper.
• For resin prints: wash in IPA, cure under UV, then remove supports.

Step 2: Sanding

Sanding is the most accessible finishing technique and works well on PLA, ABS, and PETG.

Wet Sanding Process

1. Start coarse: Begin with 120–220 grit to remove layer lines and major imperfections.
2. Progress through grits: Move to 400, then 800, then 1200 grit. Each step removes the scratches from the previous grit.
3. Wet sand: Use water with fine grits (800+) to reduce dust and get a smoother finish.
4. Finish with 2000–3000 grit for a near-mirror surface on smooth plastics.

Tip: PLA sands well but generates heat quickly — use light pressure and keep moving to avoid melting the surface.

Step 3: Priming

A good primer coat is essential before painting. It fills micro-scratches, reveals surface imperfections, and gives paint something to grip.

• Use a filler primer (like Rust-Oleum Filler Primer) to fill remaining layer lines.
• Apply 2–3 thin coats, letting each dry fully.
• Sand lightly with 400–600 grit between coats.
• Grey primer is best for most colors; white primer for light/pastel colors.

Step 4: Painting

Once primed, your print is ready for color.

Spray Paint (Recommended for Beginners)

• Use acrylic spray paint for best results on plastic.
• Apply multiple thin coats rather than one thick coat to avoid drips.
• Allow each coat to dry fully (15–30 minutes) before applying the next.
• Work in a well-ventilated area or outdoors.

Brush Painting

• Acrylic model paints (Vallejo, Citadel) are ideal for detailed work.
• Thin paints with water for smooth application.
• Use dry-brushing techniques to highlight raised details.
• Washes (thinned dark paint) add depth to recessed areas.

Step 5: Sealing and Finishing

A clear coat protects your paint job and adds the final finish:

• Matte clear coat — Natural, non-reflective finish. Great for realistic models.
• Satin clear coat — Slight sheen, versatile for most applications.
• Gloss clear coat — High shine, ideal for display pieces and figurines.

Advanced Techniques

Acetone Vapor Smoothing (ABS Only)

ABS can be smoothed chemically using acetone vapor. Place the print in a sealed container with a small amount of acetone. The vapor dissolves the surface slightly, eliminating layer lines. Warning: acetone is highly flammable — never use heat sources nearby.

Epoxy Coating

Products like XTC-3D (a two-part epoxy) can be brushed onto PLA prints to fill layer lines and create a hard, smooth surface. It self-levels and cures in 4 hours.

Filler Putty

Automotive spot filler or model putty can fill gaps, seams, and deep layer lines before sanding. Apply, let cure, then sand smooth.

Quick Reference by Goal

Post-processing is where a good print becomes a great one. With a little patience and the right materials, you can achieve results that look injection-molded rather than 3D printed.