3D Printed Concrete Molds Part 2




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In this Instructable I will go through the process I took to make a small table with Nylon Fiber infused Shapecrete and Surecrete. This was an exploration in surface treatment when compared to medium.

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Step 1: Digital Form to Mold STL

Using Fusion 360, I quickly modeled up a form that would allow me to create 4 similar but different conditions for testing surface treatment variations. Once I was happy with the form I went ahead and added holes for the mold construction roughly 1" on center.

Step 2: Assemble the Molds

These molds were designed as an arch for strength and to sit flat once poured. The 4 pieces are comprised of 2 unique forms.

Step 3: Surface Treatment (additive)

For 2 of the 4 pieces I took an additive treatment to the inside surface of the molds. Both the Zap and the XTC-3 mixtures were easy to use and brush onto the surface. Within 5 minutes of mixing the XTC-3 you can start to see the liquid get heavier and once you see the steam coming off of it, you have less than 30 seconds left. Be careful with this stuff because it does get pretty hot.

Step 4: Surface Treatment (subtractive)

For the last 2 of the 4 pieces I took an subtractive treatment to the inside surface of the molds. The smoother of the 2 I thoroughly sanded down all the rough edge. For the roughest piece among the set of 4 I wanted to try out a Acetone Vapor bath. Which consisted getting a large glass container and makeshift top (salad bowl). Using paper towels and magnets I set up a curtain around the hanging 3D printed piece to act as a surface for which to soak with Acetone. The reason for this was to have PLA plastic from the print react with the vapor that Acetone gives off in a closed chamber. I sealed the top bowl to the cookie jar with double sided 3M tape and let it sit for about 3 hours. The surface became more smooth and also very rubbery to the point that it seems like another material.

Step 5: After Math of Post Processing

Here are some up close pair shots of the pieces
1. Hand Sanded

2. Zap Z-poxy

3. Acetone Vapor bath

4. XTC-3

Step 6: Up Close Look

Here are some up close pair shots of the pieces

1. Hand Sanded - medium rough surface

2. Zap Z-poxy - smooth surface

3. Acetone Vapor bath - medium rough surface

4. XTC-3 - Super smooth surface.

Step 7: Assembling the Molds

After all the pieces were dry I began to assemble them with mini hex bolts that for the most part could be finger tightened. These do take patience but were worth it in the end to get a good solid seal to the molds. Once all the pieces come together you can get a really good feel for how large the mold is and how sturdy it will be during the pour.

Step 8: Poured Molds

Using a buckets rim I Balanced the mold one its 4 edges and poured the mixture into all 4 sides allowing it to cascade down into the center intersection. It was important to shake this very well throughout the pour as the narrowed areas combined with the few pinches of nylon fibers made it difficult to flow freely.

Step 9: Time to Demold It

First off I went ahead and cleared off all the excess concrete from the pour surface and the bolts. Once this was clear I was ready to take off all fasteners. Prying into the joints with a flat head screw driver was a little nerve racking at first but the mostly all came off easily in one way or the other.

Step 10: Analyzing the Molds

Here is where I learned the most in the process. Taking a closer look at the pieces after they were removed began to reveal where and how they either failed or impacted the concrete surface.

1. Sanding - Alone Didn't help much as it still had surface conditions that caused it to adhere to the concrete

2. Zpoxy - Created a thin film like a snake skin that it shed after the cast and but did end up easily cracking

3. Acetone Vapor Bath - Showed to be the easier to demold as it still had its rubber like qualities though it shrunk

4. XTC-3 - Had a thick smoothness to the application which helps take off the molds and was best here.

Step 11: Final Look

I was happy with the result as I got to learn a lot throughout the process. Next I will be exploring a more complex shape along with different concrete materials. Thanks for reading and stay tuned for more Slice Lab Instructables.

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    7 Discussions


    1 year ago

    For the vapor-smoothing operation I recommend using a different solvent than aceton. I did some tests a while back and DCM seems to work the best: in my tests it fully dissolved the surface layer, but it keeps together by way of surface tension. When evaporated it forms a hard shell around the object. Just put your whole setup on a hot plate to speed up the process, but be careful: if smoothed too long you might lose some of the finer features.

    Solvents Vaporsmoothing.png

    1 year ago

    for XTC, it cures with heat. a tip to make it 'last' longer while applying it is to spread it out some on a pie pan or sheet of aluminum foil. the thinner you spread it, the longer it'll last. (you'll also, obviously, lose more to the surface of the pie pan >.>)

    i believe this is true for most resins, but it definitely works with xtc. :P

    1 reply

    Reply 1 year ago

    Great idea badideasrus, I never though of that, its counter intuitive but I am excited to try it out now. Thanks!


    1 year ago

    Those comparison shots are great- easy to see how smoothing the surfaces of the mold improves the concrete finish.

    Here's an easy way to deal with the bubbles: ratchet-strap the mold down to a piece of plywood, then ratchet strap an orbital sander to the board (or glue down a sandpaper disc and stick the sander on it as you normally wood). Turn on the sander (low setting) and let it vibrate for around 30 minutes. The bubbles will rise to the top and off the surfaces of the mold.

    1 reply

    Reply 1 year ago

    Yes! Great idea with the ratchet straps. I used the a similar method of just holding an orbital sander to the surface for 10 mins.


    Reply 1 year ago

    Much appreciated 4DIYers, thanks!