Post-Processing 101: Sanding, Priming and Painting 3D Prints

A print straight off the machine is a good part. A print that has been sanded, primed and painted is a product. Post-processing is where most of the visible quality (and a good share of the time) in a finished piece lives. Here is the full sequence we use at Fantasy Lab 3D, so you know what you are ordering when you tick "painted".

Why a raw print needs any work at all

FDM printing lays plastic down in layers, typically 0.1 to 0.2 mm thick, and those layers leave fine horizontal lines on every curved or sloped surface. Resin prints are smoother but carry tiny nubs where supports were attached. Neither is a problem for a functional bracket. Both are visible on a helmet, a figurine or a lamp once light hits the surface at an angle.

Post-processing has three jobs: remove support marks and seams, hide the layer texture, and give the surface a colour and sheen that plastic alone cannot provide.

Step 1: cleanup and assembly

Before any sanding, the print is cleaned up.

• Supports are snapped or cut off; resin supports are clipped flush before final curing
• Stringing, small blobs and the seam line where each layer started are trimmed with a hobby knife
• Multi-part prints are glued, pinned and clamped so joints can be filled as one surface (details in assembling multi-part prints)

Doing assembly first matters. If you paint the parts separately and then glue them, the joint shows forever.

Step 2: sanding, grit by grit

Sanding is done in stages, each grit removing the scratches of the previous one.

Grit	Purpose
120 to 180	Knock down support scars, seams and glue lines
240 to 320	Remove layer lines on flat and gently curved areas
400 to 600	Smooth before primer
800 to 1000 (wet)	Between primer coats, for a glassy final surface
1500 to 2000 (wet)	Only for gloss finishes and clear coats

Wet sanding, with the paper dipped in water, keeps dust down and stops PLA from melting under friction. Deep layer lines and gaps are filled with a spot putty or a sprayable filler primer before the finer grits. For a detailed look at getting truly smooth surfaces, including chemical smoothing, see how to get smooth 3D prints.

Not every surface is sanded. Deliberate texture, like brick walls on a book nook or fur on a figurine, is left alone or lightly cleaned so the detail survives.

Step 3: primer

Primer is the step people skip and regret. It does three things: shows every remaining flaw under a uniform grey, gives paint something to grip, and fills micro-scratches.

• Filler primer (high-build) for FDM parts with visible lines; two or three light coats with a wet sand between them
• Standard plastic primer for resin and for FDM parts that are already smooth
• Grey for most colours, white under bright yellows and reds, black under metallics

A well-primed part should look like a single moulded object. If lines still show, it goes back to sanding rather than forward to paint.

Step 4: paint

Painting method depends on the piece.

• Spray cans or airbrush for large even surfaces: helmets, armour, vases, panels. Several thin coats beat one thick one every time.
• Brush painting for figurines, miniatures and details: base colours, then washes for shadows, then dry-brushing for highlights. We have a separate beginner guide to painting miniatures.
• Masking with tape or liquid mask for two-tone parts and crisp edges.
• Metallic paints and weathering (chipping, rust, dust) for props that should look battle-worn, like the Arthas helmet in the cover photo.

Acrylics are the standard: water-based, low odour, fast drying, and they bond well to primed PLA, PETG and resin.

Step 5: clear coat and protection

A final clear coat locks the paint and sets the sheen. Matte hides imperfections and suits armour and stone; satin is a good all-rounder; gloss is for cars, candy colours and glass effects. Clear coat also adds UV resistance, which matters for anything living near a window (more in caring for 3D printed items).

What to ask a studio for

When ordering, three finish levels cover most needs:

1. Raw: cleaned up, supports removed, nothing else. Best for functional parts and for people who want to paint themselves.
2. Primed: sanded and primed in grey, ready for your own paint. Popular with cosplayers.
3. Painted: the full sequence above, to a reference image you provide.

Fantasy Lab 3D offers all three. Painted work is quoted per piece because the time varies enormously between a single-colour vase and a weathered helmet, so send a photo of the look you want along with the model.

Ready to order?

Send the model or the idea and a reference for the finish through the contact section, and Fantasy Lab 3D will recommend a finish level and quote it. You can also DM us on Instagram at @fantasylab3d.almaty to see examples of painted work up close.