How to Salt Cure a Powder 3D Print

For a matte finish to your Z-Corp powder print, use epsom salt and water to cure the print.

I love the look of powder prints, but of course they are so fragile. Curing, or "infiltrating" the powder with other solutions makes the print stronger. You can use superglue such as Zap-A-Gap or Starbond or even epoxy to infiltrate and thereby cure Z-Corp powder prints, but these change the appearance of the material. If you want to keep the matte, powdery look of the original print, I prefer to use salt water to cure them.

This is based on instructions from 3DSystems, available here: 3D Systems User Guide

There are some other great Instructibles about curing and post-processing powder 3D prints.

Print-to-Product for epoxy-finishing

3D Powder Print Finishing with Zap CA for cyanoacrylate finishing

This print is a generative design that uses recursive polygon subdivision while referencing the original surface. This was created using Grasshopper and Python in Rhino, based on the work of Satoru Sugihara. Here is a video about creating the print design: vimeo.com/136581328

For this Instructible you will need:

A Z-Corp powder print (the print used in this Instructible is about 4.25" x 5.5" x 5.5" and is 2mm thick)

Epsom Salt (magnesium sulfate, 4 fluid oz)

Spray bottle (at least 12 fluid oz)

Wax or butcher paper for surfaces

Funnel

Goggles & gloves

A suitable area for spraying salt. Do not underestimate how much salt will get on the surfaces around your model! I used the Pier 9 Spraybooth.

The 3D Systems recipe calls for much more solution than I knew I would need. I mixed half as much salt solution as suggested.

Using a funnel and wearing goggles and gloves:

Fill the spray bottle with salt to the 4oz line,

Add warm water to the 8oz line, then

Shake the bottle until the salt is dissolved and you don't see any salt crystals. This will take a while, be patient.

With a delicate print like this one, the danger of salt curing is getting the print too wet, which will cause it to sag and even crumble. This print is especially vulnerable because it rests on just a few points.

Put down a few layers of butcher paper over a large table and lightly spritz the model from all directions.

Keep the bottle at least a foot away from the print. You want a fine mist, not big droplets.

Ideally, you shouldn't touch the print where you have sprayed it, but I carefully moved the model out of the little salt-water puddles on the table, flipped it, and put it in a new, dry area of my work table before spritzing it from the other direction.

Go slowly: the model absorbs the salt water and doesn't look visibly wet until it is too wet. Better to let it dry out and cure it again than have your print crumble.

Let the print dry at least 5 minutes before moving it as the print is extra delicate while wet.

Let the print dry for 24-48 hours.

You can see that despite my caution the print still sagged at one point. Since this print won't be handled much it is strong enough after one round of light misting.