Sticky, soft parts or residue after washing and curing

Symptom

After washing and curing, the part is still sticky or soft, resin remains in holes and corners, or thin features deform or break after washing.

Likely causes, from most to least likely

1. Not enough washing, or washing in alcohol already saturated with resin.
2. No post-cure, or the curing time, settings or unit are not right.
3. The part was cured while still wet with solvent.
4. Liquid resin is trapped in internal cavities or channels.
5. The part spent too long soaking in alcohol.

Checks to tell which one it is

• Touch the part with gloves on: if only the surface is sticky, it is usually washing or curing; if resin comes out from inside, there are cavities that were not drained.
• Think about how many parts you have washed in that alcohol: if it has been used a lot, it will be loaded with resin.
• Check whether the part was completely dry before curing.
• Check the curing: the time, that the light is 405 nm and that the unit works properly.

Before you start

Uncured resin irritates skin and eyes: wear nitrile gloves and safety glasses, ventilate the room and do not look at the UV light. Before taking anything apart or cleaning it, switch the printer off and unplug it, unless a step says otherwise. If in any doubt, stop and ask a professional.

Step-by-step fix

1. Wash in two baths

   Wearing nitrile gloves and safety glasses, wash the part in two containers of isopropyl alcohol or another washing liquid: one to remove most of the resin and a cleaner one to finish. As a guide, Phrozen gives about 1 minute in each with a soft brush; follow what your resin indicates.

   Check: Once dry, the surface has no sticky shine.

   If that does not fix it: Change the alcohol.

2. Replace saturated alcohol

   Replace the solvent when it holds a lot of dissolved resin. Formlabs, for example, says to replace isopropyl alcohol when it reaches 10% resin. To dispose of it, follow the resin safety sheet.

   Check: The part comes out of the wash clean.

   If that does not fix it: Check the drying.

3. Let it dry before curing

   Let the part dry for at least 30 minutes if you use isopropyl alcohol (Phrozen gives 30 to 60 minutes in the shade), or dry it with compressed air. Also dry the inside of hollow parts.

   Check: The part is dry to the touch, including the holes.

   If that does not fix it: Check the curing.

4. Post-cure with 405 nm light

   Cure the part with a 405 nm lamp or curing station for the time your resin recommends; as a guide, Phrozen gives about 30 minutes depending on size and shape. Sunlight also cures, but less evenly and it can discolour the part.

   Check: The part is hard and not tacky.

   If that does not fix it: Check the curing unit.

5. Check the curing unit

   If the part is still sticky with the right times, check that all the LEDs of the curing station light up and, if it has a heater, that it works. Use the curing settings given for your resin.

   Check: All the lights come on and another part cures properly.

   If that does not fix it: Contact the manufacturer of the unit or the resin.

6. Drain the cavities

   Check holes and internal channels; blow them out with compressed air or wash again to remove liquid resin before curing.

   Check: No resin comes out when you turn the part.

   If that does not fix it: Add or enlarge drain holes in the design (hollow parts sheet).

7. Do not leave it soaking

   Take the part out of the alcohol as soon as it is clean: a long soak can break parts.

   Check: Thin features keep their shape after washing.

   If that does not fix it: Shorten the washing time and follow your resin's instructions.

Prevention

• Use two washing baths and renew the alcohol often.
• Always dry the part before curing it.
• Cure with 405 nm light for the time the resin manufacturer gives.

Still not fixed?

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Printers it applies to

Any resin (MSLA/SLA) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• 3D printing post-processing FAQs · Formlabs
• Using the Form Wash · Formlabs
• Washing 3D prints · Phrozen
• Curing 3D Prints · Phrozen