3D Print Smoothing - Teracotta Air Dry Clay

Use air-drying clay to transform plastic 3D printed parts into something that looks like it is forged out of clay or as an alternative method of smoothing layer lines on your prints.

Notes:

1. This process took me about 4 months to complete. A good portion of that was because I kept putting down the project. However, I also wanted to make sure that each layer of clay dried fully before continuing, which meant letting it dry for at least 24 hours between layers.
2. The piece I tried this out on has survived two weeks with potted plants in it as of writing this tutorial (which includes watering the plants). I do not know how durable this technique will be in the long run. It's also been used on something whose only abuse is getting water in the bowl part once a week. I'm not sure I would recommend this technique for projects that require more durability.

1. Air-drying clay (I used DAS red terracotta clay)
2. Paint primer (I used a spray primer that was already the russet red like my clay)
3. Clear sealant (I used a clear gloss spraycan for decor)
4. Water-based paints (I used really cheap acrylic paint that I had lying around)
5. (Disposable) brush(es)
6. Bowl or container
7. Water
8. Glue (if you are combining prints together)
9. Newspaper or some other protective surface to work on

Use whatever FFF 3D printer you like to produce your plastic models.

If you wish to create the Indiana Jones Planter that I created, you can download the printable files here: https://www.thingiverse.com/thing:6840932

(This technique may also work on other 3D printed part types, such as SLA - I just haven't tried it)

Use the paint primer on all surfaces that you want to attach the clay to. Reminder: you probably want to have a drop cloth under your piece if you don't want primer all over your floor/table/walls.

Let the primer fully dry before moving onto the next step

Safety: If you are using a spray can, be sure to do so in a well-ventilated area and/or with a respirator with the appropriate filters. Remember: if you can smell it, it's going into your lungs!

Put down something to protect your work surface, I used newspaper.

Take a small ~2 inch ball of your clay and dissolve it into about 1/2 cup of water. You can speed up the process by manually breaking the clay into smaller chunks. For this first layer, you want an extra watery consistency so that'll more easily get into all the details and crevices.

Brush a layer onto your print. Do not worry if it doesn't cover evenly, just try to get as much coverage as possible.

Let completely dry before moving to the next step.

If you didn't first apply primer, or didn't apply enough primer, the image on the right is what your clay/water mixture will do. It's still possible to get it to stick, but it'll take some coaxing and more layers than if you had a layer of primer to grab onto.

After the super liquid-y first clay layer, add more clay and get a thicker composition. I liked one that would still slide off a spoon but only after several seconds held upright. The thicker the composition of clay to water, the less layers you'll need to apply but the more likely you'll lose fine detail.

Allow the clay to dry completely between each layer. You'll notice that when you apply a fresh layer of wet clay, it'll re-wet the previous layers, this is fine. You want the previous layer dry so that it doesn't move or get marred as much when you apply the next layer.

I gradually made my clay consistency thicker with each layer. The clay you see in the images was the consistency I used on my last layer. It was significantly thicker than the previous layers.

One of the advantages of this technique is if, like me, the print failed 20 hours in, you can easily print a replacement top and hide the mistake with an extra thick layer of clay. You can even use the clay to add features that the original print didn't have (make it your own!)

We aren't adding enough clay for it to hold the pieces together on its own, so be sure to use a glue between your prints. I used just plain old Elmer's glue on my broken top piece and to secure the snake heads on.

If you want the pieces to look like they are one piece, be sure to cover the seam with more layers of clay.

I didn't like how pink the unfired terracotta clay looked, so for the final layer of clay, I added black and brown acrylic paint into my clay/water mixture. The bowl in the image has a layer of the darkened clay, while the snakes show how much lighter the clay naturally dried to.

I also wanted my piece to look like it was old and had aged with weathering so I used a wet-wash paint technique to really darken the crevices. If you aren't familiar, you simply take some dark paint (black and/or brown) and water it down so it's like.. well... water and then you coat your piece and immediately wipe off the wet paint. The snake head on the left shows what my wet-wash looks like and the snake head on the right what it looks like after the wash has been wiped off.

This is also the step to paint your piece if that's something you want.

Let fully dry. Give it a really good LONG dry because the next step is going to seal it, and we don't want to seal in any water.

Seal the painted/clay layers with a good coat (or two or three coats) of clear paint. I used spray paint to make sure I got an even coating.

You need to create a good layer of sealant everywhere, as if the clay gets wet again, it'll get soft again and be prone to marring.

Safety: If you are using a spray can, be sure to do so in a well-ventilated area and/or with a respirator with the appropriate filters. Remember: if you can smell it, it's going into your lungs!

You're done!