Learning Hub - Finishing

Finishing & Post-Processing

Sanding, Painting & OEM Texture Matching

Transform raw 3D prints into professional-looking parts that match your vehicle's interior and exterior finishes.

Basic Finishing Process

Step 1: Sanding
Start at 220 grit, progress to 400, then 800 for smooth surfaces
Step 2: Filling
Use automotive filler primer or Bondo spot putty for layer lines
Step 3: Priming
Apply 2-3 coats of filler primer, sand between coats
Step 4: Painting
Use automotive spray paint or match with factory color code

Sanding Grit Guide

Progress through grits sequentially. Skipping grits leaves scratches that show through paint.

120-180 Grit

Removing supports, heavy reshaping

Aggressive - use carefully
220 Grit

Initial smoothing, layer line reduction

Standard starting point
400 Grit

Intermediate smoothing

After filler primer
600-800 Grit

Pre-paint prep

Wet sanding recommended
1000-2000 Grit

Polish before clear coat

Optional, for gloss finish

Primer Types

Filler Primer (Recommended)
Products: Rust-Oleum Filler Primer, Dupli-Color

Best for hiding layer lines, builds up surface

Multiple coats, sand between. The go-to for 3D prints.
Adhesion Promoter
Products: Bulldog, SEM Adhesion Promoter

PETG, Nylon, slick plastics

Use under regular primer if paint won't stick.
High-Build Primer
Products: Evercoat Slick Sand, SprayMax 2K

Deep layer lines, heavy filling needed

Professional grade, excellent results.
2K Primer (Catalyzed)
Products: SprayMax 2K, USC Spray Max

Best durability, chemical resistance

Activates chemically, superior adhesion.

Paint Options

Automotive Touch-Up Paint
Pros: Factory color match, UV stable, Durable
Cons: Expensive, Limited sizes
Best for: Exterior parts, visible trim
Spray Paint (Rust-Oleum, Krylon)
Pros: Cheap, Easy to find, Many colors
Cons: Less durable, May not match exactly
Best for: Interior parts, prototypes
Interior Dye (SEM, VHT)
Pros: Flexible, Penetrates plastic, OEM feel
Cons: Limited colors, Won't hide texture
Best for: Soft-touch interiors, vinyl/leather-like finish
Texture Spray
Pros: Hides layer lines, OEM texture match
Cons: Thick coat needed, Hard to repair
Best for: Dashboard parts, interior trim

OEM Texture Types

Match factory interior textures by identifying the pattern type first.

Fine Grain (MT-11000 series)
Medium

Standard OEM interior texture found on most dashboards

Method: SEM Texture Coating or Duplicolor Trim Paint
Soft Touch / Leather Grain
Hard

Premium interior surfaces with tactile feel

Method: SEM Color Coat flexible paint + soft touch clear
Heavy Grain (Large pattern)
Easy

Door panels, console sides, older vehicles

Method: Texture spray paint, multiple coats
Smooth Gloss
Medium

Piano black trim, modern vehicle accents

Method: Sand to 2000 grit, 2K clear coat, polish

Texture & Interior Paint Products

Texture Sprays

Rust-Oleum Textured Spray

Good for heavy grain, cheap and available

Krylon Make It Stone

Fine texture, works well for dashboard

Duplicolor Trim Paint

Designed for automotive, good texture control
Interior Paints

SEM Color Coat

Industry standard, huge color library, factory match

VHT Vinyl Dye

Penetrates plastic, flexible, good for soft parts

Duplicolor Vinyl & Fabric

Easy to find, decent color range
Clear Coats

SEM Matte Clear

Perfect for matching OEM interior sheen

SprayMax 2K Matte

Professional grade, extremely durable

Rust-Oleum Matte Clear

Budget option, works adequately

Color Matching Process

Find Your Color Code

Located on door jamb sticker, or search "[Year] [Make] [Model] interior color code"

Match to Paint Brand

SEM has the largest automotive interior color library. Search their online color tool.

Order Sample Chips

Many auto paint suppliers offer sample chips. Test against OEM part in natural light.

Test on Scrap

Always test full process on a scrap print before the final part.

Solvent Smoothing by Material

ABS

Acetone

Classic ABS smoothing. Vapor bath or brush application.
ASA

Acetone

Works like ABS. Test small area first.
PETG

None effective

PETG doesn't respond well to solvents. Sand and fill instead.
PLA

None practical

Not recommended for car parts anyway. If you must finish PLA, sand and prime.

Do's

  • Test finish on a scrap piece first

  • Sand in one direction for consistent texture

  • Use tack cloth between coats

  • Apply thin coats, multiple passes

  • Allow proper cure time between coats

  • Work in well-ventilated area

  • Match paint to OEM color code when possible

Don'ts

  • Don't skip grits - go progressively

  • Don't sand too aggressively on edges

  • Don't spray in humid conditions

  • Don't rush cure times

  • Don't use acetone on PETG or PLA

  • Don't paint without primer on raw plastic

Frequently Asked Questions

Use SEM or VHT interior paint matched to your vehicle's interior color code (found on the door jamb sticker or dealer lookup). For dashboard texture, use textured spray paint after priming.

No. PETG is resistant to acetone. The only effective finishing methods for PETG are sanding, filling, and painting. ABS and ASA can be acetone smoothed.

Heavy filler primer (4-5 coats) can fill minor layer lines. For deeper lines, use Bondo spot putty or automotive glazing putty before priming. Or use texture spray to disguise them.

Sand to 400 grit, 2K primer, automotive base coat, then 2K clear coat. This provides UV protection and durability. Alternatively, print in a color-matched ASA and just clear coat.

Partially. Use SEM Color Coat (flexible formula) with a soft-touch clear coat. The feel won't be identical to factory soft-touch, but visually it can be very close.

Allow 24-48 hours for standard spray paint to cure. 2K products often cure faster but check the label. Full hardness may take 7 days.

Troubleshooting

Paint peels or flakes off

Surface wasn't clean or primed properly. Strip with fine sandpaper, clean with IPA, apply adhesion promoter, then prime and repaint.

Orange peel texture in paint

Paint applied too thick or from too far away. Wet sand with 1000+ grit, polish, or strip and respray with thinner, closer coats.

Layer lines still visible after painting

More filler primer needed. Sand back, apply spot putty to worst areas, prime again with high-build primer, sand flat before paint.

Color doesn't match under different lighting

This is metamerism - normal for painted plastics. Match in the same lighting the part will be viewed in. Test before committing.

Texture is peeling from printed part

Adhesion failure. Strip with fine sandpaper, apply adhesion promoter (Bulldog or similar), then reprime and texture.

Can't achieve matte finish - keeps looking glossy

Some interior paints dry glossy. Apply a matte clear coat as final layer. Or lightly scuff with 1000 grit and 0000 steel wool.

See Real Results

Check out case studies showing finished parts that blend seamlessly with factory interiors.

View Case StudiesBrowse Parts Library