GoProto posted a short video of a Cerakote MJF part coated with and without primer. Two viewers asked the obvious follow-up: “What primer did you use?” and “what would be good primer options for MJF?” Nobody answered in the thread, so here’s what the coating maker and the shops that spray Cerakote MJF parts actually publish.
Do Cerakote MJF parts need a primer?
Normally, no. Formlabs’ Cerakote guide says Cerakote can reach a completely opaque solid color “without a base coat or primer.” What it does need is a properly prepared surface.
How should you prep the part?
Formlabs recommends media blasting with 100 grit aluminum oxide or garnet at 40 PSI, then wiping with a cleaner such as Prep ALL. It warns that glass bead won’t etch the surface enough for the coating to adhere. Cerakote’s own team, answering viewers under one of its 3D printing videos, gave the same number: a light blast at around 40 psi.
Don’t expect the coating to hide layers. In that same thread Cerakote said its coating is about 1 mil thick, so it may not cover layer texture. NIC’s H-Series manual puts H-Series at 1 or 2 mils.
Which Cerakote series suits MJF PA12?
Forerunner 3D, which coats printed parts, recommends oven-cured H-Series for MJF PA12 and PA12 GB, and air-cured C-Series for MJF TPU. H-Series cures at 180 °F, so it only suits materials whose heat deflection temperature is above that. HP’s PA12 datasheet lists 175 °C at 0.45 MPa and 95 °C at 1.82 MPa, both well clear.
Cerakote’s 3D printing overview lists PA12, PA12 GB, PA11, PP, TPU and TPA as MJF/SLS substrates. It marks C-Series and MC-Series for exterior or interior use and H-Series and Elite for interior use. If the part lives outdoors, that’s the line to check first.
What cure schedule applies to plastics?
NIC’s manual lists 150 to 180 °F (65 to 82 °C) for 2 hours for plastic and polymer parts, and a lower gas-out temperature for non-metals than for metal. Cerakote’s YouTube reply said 150 °F for two hours. C-Series, per Forerunner, takes 24 hours to become tack free and 5 days to reach full strength.
Before you quote a coated MJF job, blast and coat one scrap part from the same build and run a tape test on it. If adhesion fails, the blast media is the first thing to change, not the primer.
Related on the Solvi blog: How to Paint SLS Parts for an Opaque Color Match; Should You Dye MJF Parts Black or Vapor Smooth Them?; MJF PA12 Heat Resistance: Will a Thin Part Survive 60 °C?.
Sources: YouTube: Cerakote Multi Jet Fusion Part with and without Primer (GoProto), viewer questions; YouTube: Cerakote replies to viewers on 3D printed parts; Formlabs: Guide to Cerakote ceramic coating for SLA and SLS parts; Forerunner 3D: Using Cerakote on 3D printed parts; Cerakote: 3D printing industry overview; NIC Industries: Cerakote Elite and H-Series training manual; HP 3D High Reusability PA 12 datasheet.