Painting MJF Parts: Prep, Primer and Coatings

MJF nylon comes off the build a charcoal grey, and plenty of people want it some other color. Painting MJF parts is the usual fix, and it goes fine once you respect the surface you're painting.

Can You Spray Paint SLS and MJF Nylon Prints?

Yes. Get every bit of loose powder out, prime first, and lay on thin coats. Skip the primer and the porous nylon tends to drink the paint unevenly.

An r/3Dprinting thread asked this about spray painting Shapeways' nylon prints, which are SLS. The top reply matches: get "every last trace of unsintered powder" off, sand, then primer, color and sealer "in a couple of light coats each." Another said to buy spray paint labeled for plastic.

What painting MJF parts actually takes

Start with the powder. Powder-bed parts hold loose material in crevices and blind holes, and paint over it turns to grit. Blow it out, wash it, and let the part dry all the way. Nylon holds water.

Then deal with texture. As-printed MJF is a little grainy, and our post on why MJF can come out rougher than SLS explains why. A filler primer, sanded between coats, is how you get a smooth painted face. If you only want color and don't mind the texture, one primer coat is enough.

Color goes on in several thin passes. One heavy wet coat fills fine detail like embossed text and sags on vertical faces.

Paint has thickness, and that matters on functional parts. Mask bores, snap-fit faces and anything with a fit, or the fit changes.

When a coating beats paint

If the part takes abuse, a thin-film coating is worth a look. Cerakote tested its coatings on HP MJF Nylon 12 on parts HP supplied and reported 5A adhesion under ASTM D3359 Method A and 4B under Method B. That's a coating maker testing its own product, so take it as a starting point.

Dye is the other route. It adds no thickness, but color options on MJF are limited, as covered in why MJF nylon comes out grey and how evenly MJF and SLS parts dye.

From our side

MJF Nylon is on our materials page for "strong functional printed parts, housings". Painting and coating aren't on our services list, so plan to finish parts yourself, or ask us when you quote.