How do you paint and finish each kind of 3D print?

How you paint and finish a 3D print depends on how it was printed. Filament and resin prints are sanded, primed and painted; nylon powder prints are usually dyed or sealed first; metal prints are blasted, machined or polished. Paint changes colour, not shape, so most of the work happens before any colour goes on.

Still choosing between coats? Our guide to 3D print finishing compares them. Not sure which process suits your part? FDM, SLA or SLS: which is right for you walks through it.

Filament (FDM): fill and sand first

Filament printing, or fused deposition modeling (FDM), builds a part from lines of melted plastic, so its surface is a series of fine ridges. Paint does not fill them. Spray a raw filament print and you get a coloured part with the layer lines still in it.

So the ridges come out first:

1. Fill. Putty goes into the layer valleys and any marks the supports left behind.
2. Sand. The part is sanded with a firm block through 220, 400 and 600 grit until it feels even under a fingertip.
3. Prime. A primer coat shows up anything the sanding missed, and gives the paint something to grip.
4. Paint. Two or three thin coats, sanded lightly between them, then a clear coat for sheen and protection. Faces that must stay raw are masked first, though a little overspray can still reach them.

That prep is skilled hand work done at our Singapore studio, and it is most of what painting a filament part costs. Sanding softens layer lines a great deal, but a sanded filament print is still a filament print. What filling and sanding can and cannot do shows where that ceiling sits.

Resin (SLA): a light sand, then primer

Resin printing, or stereolithography (SLA), cures each layer with light at a much finer scale, so a resin part starts smooth. It still needs a light sand: the supports leave small marks where they touched, and the whole part gets a light scuff so the primer grips. Then primer, then paint.

That smooth start matters most for the two finishes that show every flaw beneath them:

• Airbrushing. Colour goes on finely enough for gradients, shading and weathering, which is why it is the finish for figurines and detailed models.
• Electroplating. A real layer of chrome, gold, copper or brass over the print. Plating magnifies every scratch under it, so it suits resin best. Electroplating SLA prints covers how it works, and metal finishes compares it with metallic paint.

Both can go on a filament part too, but only after the full fill and sand routine. See our SLA printing page for resins.

Nylon (SLS and MJF): dyed more than painted

Nylon powder prints, made by selective laser sintering (SLS) or Multi Jet Fusion (MJF), are not painted the way filament and resin are. They come out matte, slightly grainy and a little porous. Loose powder is bead blasted off, and that even, matte surface is often the finish people want.

For colour or a smoother face, these are the usual routes:

• Dyeing. The usual way to colour nylon. The dye soaks a little way into the surface, so a light scratch shows far less than it would through paint. MJF prints in black only, so other colours are dyed on request. SLS comes in grey, black or white; check with us for more.
• Vapour smoothing. Seals the pores and leaves a smoother, easier-to-clean surface. We offer it; check with us for your part.
• Sealed and painted. For an exact brand colour. The porous surface is sealed and primed first, or it soaks up the paint and the grain shows through. Paint can crack where a nylon part flexes, such as a clip or a hinge.
• Plating. Possible on nylon; check with us.

MJF comes out a little smoother than SLS, but not by much. Every nylon part is different, so ask us for more information about yours. Our SLS printing and MJF printing pages, and SLS or MJF, cover the rest.

Metal (SLM): blasted, machined or polished

Metal prints, made by selective laser melting (SLM) in 316L or 17-4PH stainless steel, AlSi10Mg aluminium or Ti6Al4V titanium, come off the machine grainy and matte. Faces that touched supports are rougher still. They are rarely painted; the metal itself is the finish.

• As printed: grainy and matte, fine for hidden or working parts.
• Bead or sand blasted: an even, matte surface with the loose grains blasted off.
• Machined faces: leave 0.5 mm of extra metal on any face that must fit, and it is machined to size.
• Polished: a smooth, bright surface.

We do not heat treat; parts are supplied in their as-printed condition. What is SLM metal 3D printing and our metal 3D printing page go further.

Big pieces: finished so joins disappear

A part too big for one print is printed in segments and joined, and the finishing is what makes it read as one piece. On a large display piece that is hand work: each segment is finished so the colours carry across the joins.

Lead times: painting adds days

As a rough gauge for a simple, low-complexity design, painted or plated parts take 12 to 18 working days for 1 to 3 parts. A batch of 15 or more takes at least 15 working days painted or 18 plated, often longer, so ask us for an accurate date.

Our instant quote includes paint in a single colour. Pick a shade from the spray paint colour catalogue, see our colour and finishing service, or ask us to recommend a finish for your part.

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