3D Print Post-Processing: Sanding, Smoothing & Painting Guide
Complete guide to 3D print post-processing: grit-by-grit sanding, ABS acetone vapor smoothing, XTC-3D epoxy coating, priming and painting. Separate section on washing and UV curing SLA/MSLA resin prints.
Your print just came off the printer looking decent. After post-processing it'll look professional. Layer lines will disappear, surfaces will be smooth, paint will apply evenly. This guide covers everything you need to know about finishing both FDM and resin (SLA/MSLA) prints.
Sanding: Removing Layer Lines
Sanding is the most universal post-processing method. The principle is simple: work from coarse grit (removing layers) to fine grit (polishing). Golden rule: never skip grit levels — scratches from 120 grit won't disappear after 600 grit, you need an intermediate 220 or 320 step.
Acetone Vapor Smoothing for ABS
Acetone vapors dissolve the outer ABS layer, fusing the layer lines together — giving you a surface indistinguishable from injection-molded plastic. Fast but requires care. Three methods: cold (room temp, 10–60 min), hot (50–56°C, 10–15 min), and brush application (selective treatment).
Hot method (recommended): pour ~1 cm of acetone into a metal can, suspend your part on a string so it doesn't touch the liquid, heat to 50–55°C. Hold 10–15 minutes, check every 5 minutes. After removal — don't touch for 30 minutes, full hardness restored in 12–24 hours. Research shows 72–81% reduction in surface roughness.
XTC-3D Epoxy Coating
XTC-3D by Smooth-On is a two-part epoxy coating designed specifically for 3D printing. It fills layer lines, cures to a hard glossy finish, and works with PLA, ABS, PETG, SLA/SLS, foam, and wood. Perfect where acetone isn't an option.
Mix ratio: 2 parts A : 1 part B by volume (or 100A : 42B by weight). Pour the mixed resin onto a paper plate — this extends working time from 10 to ~15 minutes by increasing surface area and reducing heat. Apply with a foam brush in thin coats. Tack-free in 2 hours, full cure in 3.5 hours at 23°C. 1 oz mixed covers 651 cm².
Priming and Painting
Primer is mandatory before painting. It ensures paint adhesion, reveals remaining defects, and evens out the surface. Filler/sandable primer is the best choice for FDM prints: it's thicker than standard primer, fills fine scratches, and sands easily.
Process: apply 2 coats of primer at 15–20 cm distance with quick passes. Let dry, wet sand with 500–600 grit, re-prime if needed. Then acrylic paint in 2–4 thin coats with 20–30 minutes drying between layers. Finish with 1–2 coats of clear coat (matte/gloss/satin). After clear coat, let the model rest at least one week before heavy use.
Resin Post-Processing (SLA / MSLA / DLP)
Resin printing requires a specific workflow. A freshly printed part hasn't reached full strength and is coated in liquid resin. The correct sequence is critical.
What Works with Which Material
| Material | Sanding | Acetone | XTC-3D | Painting |
|---|---|---|---|---|
| PLA | ✓ 120–1000 grit | ✗ Doesn't work | ✓ Excellent | ✓ Primer required |
| ABS | ✓ 100–1000 grit | ✓✓ Best method | ✓ Works | ✓ Acrylics |
| ASA | ✓ 100–1000 grit | ✓✓ Like ABS | ✓ Works | ✓ Acrylics |
| PETG | ✓ 100–1000 (wet!) | ✗ Ineffective | ✓ Works | ✓ Acrylics |
| Resin SLA | ✓ 220–2000+ (wet only!) | ✗ N/A | ✓ After curing | ✓ After curing |
| Nylon | ✓ 120–600 grit | ✗ No reaction | ✓ Epoxy | ~ Difficult |
Post-processing turns a 'printed part' into a 'finished product.' Start with sanding — it works for all materials and sets the foundation for every next step. For ABS, add acetone smoothing. For PLA, epoxy coating. Priming and painting finish any model regardless of printing technology.