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I've been experimenting with FDM 3D printers and PLA for about a year now. I'm at the point where I'd like to produce something considerably stronger than PLA, and was wondering if there is a faux-pas list, or general instructions on how to coat PLA with epoxy resin, or even fibreglass/carbon fibre and resin to add strength and a surface to sand and paint.

I would have assumed that I'd need to coat the PLA object using a brush and epoxy resin, but I've also seen blogs where the epoxy mix has been heated enough to become liquid and then the PLA object was submerged in it.

Obviously the fibre coating would most likely have to take place manually by adding sheets, unless I decide to go for shredded fibres (which probably won't provide the strength I'm interested in).

Has anyone tried it, or have a guide on how to do this?

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  • $\begingroup$ Have you considered printing in a different, stronger material rather than coating it? Know that there are also fibre reinforced nylon filaments available. So, is the question still directed to a coating or stronger print? $\endgroup$ – 0scar♦ Dec 2 '19 at 15:40
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    $\begingroup$ @0scar I have, unfortunately my current setup doesn't allow me to do so. Furthermore this question isn't only about strength, but also about the finish the object will have. For example, coating it with epoxy would allow me to treat it differently (spraying, painting, even electroplate it). I've seen carbon filaments which are prohibitively expensive and still won't reach the strength of a CF reinforced object. $\endgroup$ – Ælex Dec 2 '19 at 15:55
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    $\begingroup$ Fair enough, let's see what post processing answer this generates! Welcome to 3DPrinting.SE! :-) $\endgroup$ – 0scar♦ Dec 2 '19 at 16:01
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    $\begingroup$ It would be interesting to see a resin that could hold the shape of a PLA print in high temps. Maybe a two part resin, mixed together, painted on at room temp, that would harden and hold PLA's shape up to like 250 C. PLA is just so easy to print $\endgroup$ – K Mmmm Dec 2 '19 at 19:21
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    $\begingroup$ @KMmmm We call that concrete! ;-) $\endgroup$ – 0scar♦ Dec 2 '19 at 19:54
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I have used Styrol based Polyester resins on prints and they created the usual stench as well as a surefire bond and it is easily useable with unstructured fiberglass, as that fiberglass has usually a binder that will react with the styrol and bond the mat.

Epoxy resins also bond nicely to PLA and don't have the styrol smell, but they are not bonding that nicely to normal fiberglass, you want to use them with fiberglass weave.

Either resin is a quite viscous fluid. When you cast a flat surface, it will try to smooth out to a good degree under gravity. When coating a curved surface, you should make sure to align it in way that the lowest point is either the top of the dome or the lower edge, so it settles equally. You can aid in this process by providing heat as this will lower viscosity. An airstream will also aid as it presses onto the surface helping to smooth out unevenness.

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