Post-Processing 3D Prints: Sanding, Painting & Finishing Guide

Your print just finished. It has visible layer lines, a rough bottom, and looks... well, like a 3D print. Post-processing is the difference between a cool prototype and a professional finished piece. Here's our complete guide, tested and refined on hundreds of prints at our Roy, Utah workshop.

Step 1: Removing Supports

The first step after a print finishes is removing any support material.

• Use flush cutters or side cutters — don't try to snap supports off by hand (you'll gouge the print)
• Leave a tiny gap — cut about 1–2mm away from the print surface, not right against it
• Sand the nubs flush — 220 grit sandpaper takes care of remaining support marks
• For PLA supports — let the print cool completely first; warm PLA tears more easily

Step 2: Sanding

Sanding is the single most impactful post-processing step. Here's the progression we use on every display-quality print:

120 grit	Heavy material removal, leveling major imperfections
220 grit	Smooths 120-grit scratches, removes layer line ridges
400 grit	Prep surface for primer/painting, removes fine scratches
600+ grit	Final polishing prep (optional, for painted pieces)

Sanding Tips

• Wet sanding reduces dust and gives a smoother finish — use water with a few drops of dish soap
• Sand in one direction with each grit, then switch direction for the next grit so you can see when previous scratches are gone
• Don't skip grits — going 120 → 400 directly leaves deep scratches that show through paint
• PLA sands beautifully; PETG is a bit gummier; ABS and ASA respond well to chemical smoothing

Step 3: Filling Gaps & Imperfections

For prints where you need a glass-smooth surface:

• Automotive body filler (Bondo) — fills layer lines and gaps. Apply thin, sand with 400+ grit after curing (~30 min)
• CA glue (super glue) — surprisingly effective as a thin filler. Apply with a brush, sand after it cures (~10 min)
• 3D printing primer/filler — products like Rust-Oleum Filler Primer fill minor layer lines while priming for paint

Step 4: Chemical Smoothing (ABS/ASA)

Acetone vapor smoothing is the magic trick for ABS and ASA prints:

1. Place the print in a sealed container (glass or metal)
2. Add a small dish with acetone — don't pour acetone on the print directly
3. Wait 10–20 minutes — the vapor melts the outer surface
4. Remove and let dry completely (1–2 hours)

The result: glossy, injection-molding-quality surface with zero visible layer lines. This doesn't work on PLA (acetone doesn't affect it), but for ABS and ASA it's transformative.

Step 5: Priming & Painting

Whether your print is a gift, a cosplay prop, or a functional painted part:

Priming

• Use a filler/automotive primer spray — it fills remaining texture and creates a paintable surface
• Apply 2-3 thin coats with 15-minute flash-offs between (thick coats drip)
• Lightly sand with 600 grit between coats for the smoothest finish

Painting

• Acrylic paints (like Vallejo, Apple Barrel) for hand-painting details
• Spray paint (Rust-Oleum, Montana) for large-area coverage
• Airbrush for professional-level gradients and fine detail work
• Seal with clear coat — matte, satin, or gloss depending on the final look you want

Pro Paint Tip

Heat your PLA print slightly (35–40°C) before spraying. This prevents thermal shock from cold spray hitting a cold print and improves paint adhesion. A hair dryer on low works great.

Post-Processing Tools We Stock

At Forgely Roy, we carry the essentials for post-processing success:

• Flush cutters and hobby knives
• Sanding sponges and sandpaper (assorted grits)
• Primers and spray paint in popular colors
• CA glue and body filler
• Dry boxes for filament (dried filament = smoother prints = less post-processing)

Utah Tips

Our dry climate in northern Utah actually helps post-processing — paints cure faster and primer dries quicker than in humid states. Just work in a well-ventilated area, especially with spray paints and acetone.

Visit Forgely Roy for Post-Processing Advice

We're happy to demonstrate techniques in person or recommend the right products for your specific print. Stop by the shop and we'll show you what works.

📍 5519 S 1900 W, Roy, UT 84067
📞 385-449-2694
⏰ Mon–Fri 11–6 • Sat 11–3