Washing and Curing Resin Prints: How to Do It Right
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A resin print is not finished when it comes out of the printer. It is coated in liquid resin and not yet fully cured. Three steps follow: wash, dry, post-cure. Wear gloves and safety glasses while doing so, as described in Resin printing safety.
1. Washing
With what: you wash most resins with isopropanol (IPA). Formlabs recommends a purity of at least 90 %, Phrozen and Elegoo give 95 %. For water-washable resin, water is enough. There are also special washing solutions that are not flammable, for example the Resin Washing Solution from Formlabs with a flash point of 93.5 °C.
Two baths: a pre-wash bath and a clean final wash bath have proved their worth. In the first, most of the resin dissolves, and in the second the part gets really clean. With every wash the resin content in the IPA rises, and at some point you have to replace it.
How long: this depends heavily on the resin, and the figures differ widely.
| Manufacturer | Recommendation |
|---|---|
| Phrozen (hobby resins) | two tanks, about one minute each; in the wash station at least 30 seconds, but under 3 minutes per cycle |
| Formlabs (own resins) | two baths of 10 minutes each, moving the part between them |
According to Phrozen, soaking in alcohol for too long can make parts brittle. Follow the data sheet of your resin.
Wash and cure stations
Combination devices wash and cure in one machine. In the Elegoo Mercury Plus, for example, a stirrer that changes direction regularly turns in the closed container with up to 3 l of IPA. For curing you take the container out, and the part rotates on a plate under UV LEDs. The LEDs only switch on when the lid is closed. Such stations save time and keep the IPA covered.
2. Drying
Before you cure, the part has to be completely dry. Formlabs gives at least 30 minutes, Phrozen 30 to 60 minutes in air in the shade. Compressed air or a fan speeds this up. If you cure a part that still has IPA with dissolved resin in it, according to Formlabs the solvent is trapped inside, the part does not become properly solid, and the material properties suffer.
3. Post-curing
Post-curing under UV light brings the part to its full strength. With standard resins it is optional according to Formlabs, and with functional resins it is necessary. There is no general time, as it depends on the resin, the lamp and the part size:
- Elegoo sets the time on the Mercury Plus in 30-second steps and stresses that it differs for each resin.
- For its Cure Mega curing chamber, Phrozen gives “one hour or less”.
- As an example, Prusa gives 3 minutes in the CW1S after drying at 45 °C.
Turn the part at least once so that all sides get light. And do not overdo it: according to the resin manufacturer Power Resins, overcured resin becomes more brittle. Parts that then lie in the sun continue to cure.
Removing supports
Formlabs recommends snipping off the supports only after post-curing, because soft parts without supports can warp under light and heat. Wear safety glasses while doing this, as small supports fly off.
Sources
- Formlabs Support: Choosing a solvent, Basic post-processing, Using Form Cure, Using Form Wash, Which post-processing is required
- Phrozen Helpcenter: Washing 3D prints, Cure Mega (no longer online)
- Elegoo: Yellowing of transparent resin
- 3D with us: Elegoo Mercury Plus
- Prusa: Resins and safe SLA printing
- Power Resins: Brittle prints