Post-Processing 3D Prints: Sanding, Smoothing & Priming
The gap between a rough print and a display piece is finishing. Here's how to sand, fill and prime FDM and resin figures for a smooth, paint-ready surface.
A print straight off the bed shows layer lines and support marks. Ten minutes of finishing turns it into something that looks bought, not made in a garage. Here's the workflow.
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Finishing does two things: it removes visible layer lines and blemishes, and it gives paint a smooth, even surface to grip. Even if you print in color with an AMS, a light finish lifts the result.
Sanding
- Work up through grits: start around 220, then 400, then 600+.
- Wet-sand to reduce dust and clogging, especially on PLA.
- Go gently on fine detail — sanding flattens sharp features fast.
Filling and smoothing
For stubborn layer lines or gaps, use a filler primer or a thin coat of automotive spot putty, then sand back. Several thin passes beat one thick one.
Priming
Primer unifies the surface and reveals flaws you missed. Spray thin coats from ~20 cm; grey primer is the most forgiving. Once primed, you're ready to paint.
Resin specifics
Wash and fully cure resin prints first. Cured resin sands cleanly but produces fine dust — always wet-sand and wear a mask. Resin detail is sharp, so you'll usually sand only support nubs and the raft contact area.
Getting a smooth or glossy finish
If you want a factory-smooth look, work through the grits patiently and finish with a filler primer, sanding lightly between coats until layer lines vanish. For a glossy toy-like finish, seal with a gloss varnish at the end rather than trying to polish the plastic directly. Matte varnish, by contrast, hides small imperfections and reads as more premium on character figures.
Work clean and safe
Always wet-sand and, for resin, wear a mask — fine plastic and resin dust are irritants you don't want in your lungs. Work over a tray to catch grit, keep cured resin scraps out of drains, and dispose of IPA and resin waste according to local rules. Good habits here cost nothing and keep the hobby enjoyable.
FAQ
How do I remove layer lines from a 3D print?
Wet-sand up through grits (220, 400, 600) and apply a filler primer, sanding back between coats. This hides most FDM layer lines before painting.
Do I need to sand before painting?
A light sand and a primer coat make paint adhere far better and look smoother. For color AMS prints you can skip heavy sanding, but priming still helps.
Is sanding resin prints safe?
Only after full cure, and always wet-sand with a mask - resin dust is an irritant. Cured resin sands to a very smooth finish.
