A few weeks ago, I read the announcement that Smooth-On had launched a product for post processing 3D printed objects to help smooth the layers called XTC-3D. From their product page, here is the description and the performance claims:

XTC-3D® is a protective coating for smoothing and finishing 3D printed parts. Two liquids are mixed together and brushed onto any 3D print. Coating self-levels and wets out uniformly without leaving brush strokes. Working time is 10 minutes and cure time is about 4 hours (depending on mass and temperature). XTC-3D® cures to a hard, impact resistant coating that can be sanded, primed and painted. Adding colors and metal effects is easy. Inexpensive to Use: 1 oz covers 100+ square inches. 90% Time & Labor Savings: XTC-3D® fills in 3D print striations and creates a smooth, high gloss finish. The need to post finish is almost eliminated. Coat any 3D Print Surface: XTC-3D® can be applied to both SLA and SLS prints. It works with PLA, ABS, Laywoo, Powder Printed Parts and other rigid media. It also can be used to coat EPS, EPDM and urethane foam as well as wood, plaster, fabric, cardboard and paper. XTC-3D® does not contain VOC's, phthalates or phosphates.

This sounded like a pretty interesting proposition to me. Given that the excellent PLA vapor smoothing solvent I came across a few months ago appears to be discontinued, I was particularly interested in this as a potential for easy preparation of parts for lost PLA investment casting or mold making.

So I placed an order and it showed up a few days later.  Here's what was in the box:

I tried it out on several prints I had around in different materials. A Celtic Skull, Grumpy Pumpkin, Robot Card Holder, and half globe in colorFabb Pale Gold PLA/PHA, all printed on an Ultimaker original at 100-200 micron layer height. Tiki Pencil holder in woodfill, printed on a Robo3D Beta PLA edition at 254 micron Layer height. A Make Robot Charm printed in colorFabb BronzeFill on an Ultimaker at 100 micron layer height, and a Moai head printed on a Robo3D R1 at 200 micron layer height. The Make robot had been tumbled with glass beads for about 24 hours, so it was quite smooth going in. The Moai was simply burnished a bit with coarse grit steel wool to get some shine.

All of the parts were then set out on a paper plate on my dining room table in preparation.

I proceeded to mix up about 30ml of XTC-3D solution per the instructions… well, mostly per the instructions. I didn’t really pay attention to the bit about the well ventilated area. This was a mistake. This stuff has extremely high odor. So, I slid the table closer to the window and opened it up regardless of the Arctic Bomb Cyclone weather pattern we have going on.

Shortly after mixing, I began coating the parts as quickly as I could to stay within the 10 minute working time. First few parts coated well (the pumpkin and the half globe) with a very good viscocity. By the time I got to the last parts, the tiki, the make robot, and the skull, it was pretty much too thick to work with. I didn’t have a timer going, but I’d guess it wasn’t near the 10 minute working time. Probably closer to 5 minutes.  Worth noting is that everything looked pretty awesome while it was still wet.

The parts were then allowed to cure overnight, IN A WELL VENTILATED AREA.

Here are pictures of the fully cured/dried prints with some discussion in the captions.

I had a bunch of those pale gold pumpkins printed so I got some good side by side before and after shots and also did the Play-Doh test.

 Overall, I’m lukewarm on this material.  I certainly would not discourage someone who wanted to try it.  It's reasonably priced and will go a long ways.  However, I don’t think that it is going to be a great option for investment casting or mold making where you really want to preserve all of the detail of a complicated print. Printing at a high resolution and then sanding or polishing seems to remain a better option for this type of print as it preserves detail while removing layer lines.  It probably would be handy for preparing prints with coarser geometry.  It's also worth noting that it seemed to do a better job at improving the quality of poor quality prints than smoothing prints that were already very good.

I could see some value in this material or other similar coatings for other applications. One would be to make PLA parts more heat tolerant. Since the epoxy is a thermoset, I would not expect the deformation with temperature you see with PLA.  More tests will be forthcoming to test this idea out.  As long as it doesn't crack when the PLA hits it's glass transition temp, it could be really useful.

The other would be preparation prior to painting. I think this probably does a better job of filling in layers than spray on filler primer and also leaves the option of masking off areas to leave the original plastic color intact.  This isn't really something that I do, so I didn't explore it at all.

Mixing in metal powder, pigments, or other materials to get different effects might also be interesting to explore further.