Washing and Curing Resin Prints

A print fresh off the build plate is coated in liquid resin and is not fully cured. Washing removes the liquid; post-curing finishes the solid. Wear your resin PPE through the whole wash, because the part, the solvent and the container all carry liquid resin (see Resin PPE).

1. Pick the wash liquid your resin calls for

• Isopropyl alcohol (IPA). The common choice for standard resins. Formlabs says most of its resins can be washed in IPA of 90 percent or higher concentration Maker spec, and biocompatible Formlabs resins need 96 percent or higher. Those are Formlabs' numbers for Formlabs resins; use your resin maker's figure.
• Other solvents. Formlabs also uses TPM for some workflows. Use only what your resin maker lists.
• Water, for water-washable resin. The resin is formulated to rinse in water. It is still resin: the Anycubic Water-Wash Resin+ SDS lists it as a skin sensitizer that causes serious eye damage and may irritate the airways, and says not to let it enter surface water or drains. Gloves and eye protection apply, and the used wash water must not go down a drain. See Resin Waste and Disposal.

IPA is flammable. Formlabs says to use and store it away from ignition sources, work in a well-ventilated area and handle it in nitrile or neoprene gloves. Prusa warns that IPA is a volatile flammable liquid and says not to leave the lid closed while the IPA container is in its CW1 machine. Keep IPA in labeled, sealed containers.

2. Wash: the maker's time, not longer

Wash times are set per resin and per machine. Two makers show the spread:

Maker and setup	Wash guidance
Formlabs, manual Finish Kit	For most Formlabs resins, two 10-minute soaks in separate baths, with 30 seconds of movement by hand Maker spec; some of its resins need shorter washes, so check the resin's own table
Prusa CW1 wash machine	3 minutes by default; do not wash in IPA for more than 10 minutes Maker spec

Prusa explains why there is a ceiling: parts washed too long in IPA can develop tiny surface cracks, sometimes more than 24 hours later. Formlabs says to wash longer when the solvent is more saturated with resin and shorter for small parts. Both point the same way: check your resin's own table and wash until clean, not indefinitely.

The two-bath method in Formlabs' kit is easy to copy with any two lidded containers: a first, dirtier bath takes most of the resin and a second, cleaner bath finishes the part. When the solvent stops cleaning well, replace it. Formlabs replaces IPA when its hydrometer shows 10 to 12 percent resin concentration Maker spec; that hydrometer is part of Formlabs' wash station.

Hollow parts need their insides washed too; see Hollowing.

3. Dry completely before curing

Formlabs says to always let prints dry fully before post-curing, whether they were washed in IPA, TPM or water, and to allow at least 30 minutes for IPA to evaporate Maker spec with ventilation while it does. Forced air speeds this up.

4. Post-cure

Post-curing exposes the part to UV light (in many curing stations, with heat) so the resin reaches its finished properties. Formlabs says post-curing is optional for its standard resins but required for other resin types to reach their optimal mechanical properties. Follow your resin's data sheet for the cure time, and the temperature if it gives one.

• Prusa CW1: drying and curing are set to 3 minutes each by default Maker spec, which Prusa says works for most objects. If a part is still a little sticky, Prusa says to run the process again. Place the part near the edge of the turntable, not the center, and keep the lid closed; the lid has a safety switch.
• Other stations: use the resin maker's cure table for that station.

A print that stays tacky after washing and curing has its own causes; see Sticky Resin Prints.

5. Supports: after the cure

Formlabs recommends removing supports after post-curing, because a part without supports may warp under the light and heat of curing. Cut close to the surface with flush cutters and wear eye protection (see Orientation and Supports).

What happens to the dirty solvent

Used IPA or wash water holds dissolved resin. Formlabs says IPA containing dissolved resin must not go into drains or household waste, and the Anycubic water-wash SDS says the resin must not enter drains. How to dispose of it depends on where you live: see Resin Waste and Disposal.