Post-curing Underwater

On the support page for the flexible resin there is a small paragraph on finishing when using this material:

“If your part still feels tacky after washing in IPA, try post-curing it underwater. Find a clear glass container, place your part in the container, and cover it with water. Leave the container out in the sun until it no longer feels tacky to the touch.”

Post curing underwater? I haven’t seen this being recommended before. Anyone know why this is a benefit? Is it recommended for other resins as well?

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The post below explains it. I have been following this method and it works like a charm, At night I use my UV oven.

“The reason the print is left feeling sticky is due to the outer surface not fully curing. This is because of the presence of oxygen, which stops the curing of the outer layer. By placing the the print in water and exposing it to UV light, you are limiting the amount of oxygen diffusing into the uncured resin, which allows it to fully cure. The water is essentially acting as an oxygen barrier.”


Perfect! Thank you. I’ll give it a try

Works like a charm too. If you use a curing box combined with water you can close to fully cure a part in 10 minutes or less. But it can result in a hazy surface finish.

Would it work on regular resin or this is really only for the flexible resin?

Any resin.

I had a thought of trying a Dental sterilizer? Dental sterilizers are ultrasonic cleaner and UV sterilizer combined.

The ultrasonic cleaner would clean surface and any internal structures and the UV would cure the resin,

Here is an example.

I’m getting ready to try my first print with Flexible resin. This post-curing trick will work great with my budget UV curing jar. UV LEDs on the outside of a clear acrylic jar. Fill it with water, no problem. Perfect, no?

I tried post-curing the black resin under water over the past week – it works amazingly well! I’m not sure why this isn’t more prevalent in the Formlabs documentation.

So… for the black, it actually turns the print grey. You have to use mineral spirits to get it back to black (if anyone is really picky about the color). It also seems to make the prints a lot more chalky versus the standard cure. To me, I like the chalky behavior better – somewhat ironically, they feel sturdier than the non-water’d parts.

(For the life of me, I couldn’t find out how to start a new topic on the forum… so decided to reply to this related one)

We’ve been having great results with the underwater curing, but of course we end up with quite a lot of contaminated water. At least, I assume it’s pretty unhealthy stuff that shouldn’t just go down the drain. Does anyone have a great idea for how to deal with this responsibly?

I suspect it might be ok to pour it down the drain, as the material is fully cured, and it ought to get filtered out. On the other hand, I have been reluctant to do this, as it just feels wrong, and it being summer, I just leave the water outside (somewhere where animals won’t get to it - my printer is in a basement and I have a really handy shaft outside the window with a grate over it) and it evaporates leaving a residue behind; you can pour the water into a plastic container which you can later throw away with normal rubbish which frees up the original curing container; this I rinse with a little alcohol before refilling with water.

I 've noticed you can cure quite a lot with just one jar of water - I just use it until it is so cloudy it feels like UV couldn’t be penetrating anymore. So I’ve been saving up a few jars of ‘formlabs water’ and labeled it and then I bring them along on my trip to the recycling centre every few months. I assume they have a better chance of taking care of it responsibly.

Seagull hit it on the nose.

Liquid resin should never be poured down the drain, and cured resin could potentially cause clogs. Straining the water and throwing away the cured resin as normal waste would be my recommended approach.


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I’ve had quite some problems with sticky parts.
Now I’ve started to use this method.

I only rinse in IPA for about 2 minutes now than dunk it in water and put it in daylight (or under the UV lamp but I have had good weather recenty so no need for the lamp).

The parts cure really fast and clean. Surfaces look better (because I’m not washing out so much resin on the surface I think) and seem to be less brittle (probably because of the shorter time in IPA).

So I’d call it a full success!

I have not tried the water cure method yet, as my parts are coming out hard enough after IPA + Water rinse and then letting them sit in a bright room for a day or so…

I also found i did not need to soak the parts long at all… Slosh around in the container of 91% IPA for 2mins, let sit for another 2, then shake again for 30 seconds. Wash parts under water and use a tooth brush with fine bristles to brush the part.

Have been having really good success with this method.

I might be misunderstanding this so if someone can clarify;

After finishing my print and cleaning it with IPA, I should submerge my print in tap water and leave it under the sun for about 30 minutes. This is how you guys do it right?

Yes, that will work

Might depend on your tap water, I just recently tried that method, and we have very hard water. The print started very clearly leeching calcium out of the water, and getting grey spots all over the surface. At least with my tap water, just UV curing without water is the better option.

Alright. Thanks guys(@Zachary_Brackin & @lmlloyd ) will try and see how my tap water works here. Otherwise I might make one of those cheap UV light boxes.

The UV box is just for convenience, because you can do it at any time. Otherwise you have to do it during the day and make sure that it doesn’t stay in the sun too long.