PETG prints can be sanded, coated and bonded, but heat and solvents can change the surface or distort a close-fitting part. Start with the required appearance and joint strength, then test the finishing method on a spare print. This guide covers sanding and polishing steps, coating, bonding and common finish problems.
Why Post-Process PETG?
Raw PETG prints have visible layer lines and may not meet aesthetic or functional requirements for final products. Post-processing can:
- Improve surface smoothness for visual appeal
- Increase strength through better layer bonding
- Create waterproof seals for functional parts
- Enable painting and finishing
If you’re still deciding between materials, post-processing capabilities might influence your choice.
Sanding PETG
Starting Point
PETG sands well but is softer than PLA. Begin with:
1. 200-400 grit — Initial layer line removal
2. 600-800 grit — Smoothing transition
3. 1000-1500 grit — Final polish preparation
Technique Matters
Always sand in circular motions rather than back-and-forth. This prevents directional scratches that become visible after finishing. Wet sanding reduces heat and clogging.
Progression Example
| Bühne | Grit | Time (small part) | Result |
|---|---|---|---|
| Rough | 240 | 2-3 minutes | Layer lines removed |
| Mittel | 400 | 2 minutes | Surface smooth |
| Fine | 800 | 1-2 minutes | Matte finish |
| Polish | 1500 | 1 minute | Glossy appearance |
Chemical Smoothing
Unlike ABS, PETG doesn’t respond to acetone vapor. However, alternative methods work well:
Heat Gun Smoothing
A carefully controlled heat gun can smooth PETG surfaces:
1. Set heat gun to 200-250°C
2. Hold 15-20cm from surface
3. Move continuously in sweeping motions
4. Stop when surface glosses but before deformation
ABS users with acetone experience will find this technique different but manageable.
Epoxy Coating
A thin epoxy coating creates a smooth, glossy finish:
1. Sand to 400 grit minimum
2. Clean surface with isopropyl alcohol
3. Apply thin epoxy layer
4. Allow full cure (24 hours)
5. Sand lightly with 2000 grit if needed
Bonding PETG Parts
Large prints often require multi-part assembly. Here are proven bonding methods:
Super Glue (Cyanoacrylate)
Works well for small, non-stress parts:
- Clean surfaces with alcohol
- Apply thin, even layer
- Hold parts in position for 60 seconds
- Full cure in 24 hours
Epoxy Bonding
Best for structural applications:
- Rough surfaces with 120 grit
- Mix epoxy per instructions
- Apply to both surfaces
- Clamp during cure
- 24-hour full cure
Plastic Welding
Creates strongest bonds by melting material together:
- Use PETG welding rod or cut filament
- Heat gun or dedicated plastic welder
- Practice on scrap first
- Fill gaps completely
Production-scale projects benefit most from welding.
Filling and Painting
Priming
After sanding:
1. Apply plastic primer spray
2. Light, even coats
3. Allow flash time between coats
4. Sand with 600 grit before color
Malerei
PETG accepts most paints well:
- Acrylic paints brush-on easily
- Spray paint provides smoothest finish
- Clear coat protects finish
- Avoid solvent-heavy paints
Troubleshooting
Sanding discolors my print
This indicates excessive heat. Wet sand to cool the surface, or use lower grit more gently.
Chemical smoothing doesn’t work
PETG requires different chemicals than ABS. Heat-based methods work better.
Bond fails under stress
Use epoxy or welding for structural bonds. Super glue isn’t suitable for stress applications.
Häufig gestellte Fragen
Can PETG prints be sanded and polished?
Yes. Work through progressively finer abrasives and keep heat low; wet sanding can reduce clogging and surface smearing. Test the finish on a spare print before treating a visible part.
Will acetone vapor smooth PETG?
PETG does not respond to acetone vapor like ABS. For a smoother appearance, consider careful sanding followed by a compatible coating, and test the finish first.
What is the best way to bond two PETG parts?
The choice depends on joint load and fit. Cyanoacrylate can suit small lightly loaded joints; a compatible epoxy or PETG welding may be considered for other assemblies. Prepare and test the actual joint before relying on it.
Can finishing affect PETG dimensions or strength?
Yes. Sanding removes material, heat can deform features, and a coating adds thickness. Define critical dimensions and joint loads before finishing and inspect the finished part.
