3D Printed Concrete Molds

Hello! This instructable will (hopefully) show you how to create a vase out of concrete, but more importantly, it will illustrate the concept of a 3D printed mold. This project cost $7.50 not including the printer and filament. I wanted to use this project more or less as an experiment in 3D printing molds for concrete, so I figured I would design my own vase to illustrate this. The beauty of 3D printing is that you can create as much as your printer can handle and with this technique cast as much as the printer can handle as well.

1. Computer with 3D CAD software(I used SolidWorks)
2. A 3D printer with appropriate software (I used a MakerBot)
3. Concrete

For this project, I used a MakerBot Replicator 3D printer and ABS filament. Below I will attach a link to the STL. for the vase I created the mold in SolidWorks and exported it to STL afterward, then put it into the MakerBot software. It was a fairly large 3D print for me and it took about 8 hours but I'm happy with the way it came out. But again the beauty of this is that you design your own mold, so you can make it as big or small as you want.

When creating your mold in CAD make sure to not make the object you are creating but rather a cutout of the object into a block or cylander or other shape. This kind of means you have to think backwards when creating it.

If your print/printer is anything like mine, the mold itself is actually porous, which isn't great for concrete because when it sets it will cling to the sides and not come out of the mold. So I coated the inside of the mold with petroleum jelly which simultaneously acted as a sealant and lubricant, so it would be easier to take out. Also for my mold I had to use some old plastic tubes to ensure the inside would stay waterproof, and those create the cavities that

As I mentioned I used Quickrete Fast Setting Concrete which comes in a bucket, but, somewhat deceptivley it came in a bag, so I emptied the bag into the bucket. The powder that comes out of the bag is VERY fine and gets everywhere. If you are doing this indoors make sure to lay down some sheets or a tarp so you don't get all over your floors.

The little label on the side of the bucket says that your ratio of water to concrete should be about 5.5:1. I mixed according to that ratio and it turned into a slurry the consistency of icecream and was pretty hard to pour into the mold. I didn't mix enough so I ended up mixing a second batch with more water (it was the consistency of semi-melted ice cream) and that poured much easier.

After filling the mold, I vibrated out the air bubbles in the mold. I then took a tiny utility knife and traced the outline of the vase so it wouldn't cure with the overflowed concrete. Make sure to do this because it is quite the pain to cut concrete cleanly without the proper tools. Then I just let it sit. The package said that the concrete set in 10-20 minutes but given how densely I was packing it, I didn't want to take any chances so I just left it in the mold overnight

OK. This is probably the hardest part. Despite the petroleum jelly, the concrete was pretty hard to remove. What I did is I held my hand over the exposed concrete and heated up the mold under hot water so that it would expand. I then lightly tapped all the faces of a mold with a hammer and repeated until the mold came out. Of course if you wanted to you could break the mold, but I wanted to see if I could preserve it.

Chances are, once removed from the mold, the object will be pretty rough. If you use a coarse sand paper, you can sand and shape the concrete how you want. I used it to create a small pedestal on the bottom, that kind of seems to lift the vase off of the ground. Other than that though, I didn't do much finishing. I liked that worn/wrought look of the concrete. But of course it is up to you.

First of all, thank you so much. I hope you enjoyed either making or viewing this instructable. Your feedback, thoughts, and questions are appreciated. As I said at the beginning of the instructable, this was half a project and half an experiment. I had never used concrete to build anything before, and I wanted to try it out and the concept of molds made in any shape appealed to me so I embarked on this test. If I did this again, I would have used a smaller mold and shrunk the walls to optimize filament use. I would not have used the quick setting cement because it sets even while mixing. Next I probably want to try something more complicated. Thank you again! Please post comments below.