I made the structure! Yay! It was super frustrating and took way too long, but I did it. Let me tell you the story with pictures and several words…
I coated the mold for the base with WD-40.
Then I mixed up a batch of fast setting concrete.
Naturally, the stick I was using to stir broke, and I didn’t have time to grab gloves.
I got it nice and mixed, then poured it in. I didn’t have enough.
Also, I didn’t bother to read the can of WD-40. It dissolves adhesives. Having let it sit while I mixed the concrete gave the tape and hot glue plenty of time to loosen. Thankfully, only one of the sides split off, rather than the whole thing falling apart on me.
I was already out of concrete, so I let the thing sit for a couple days while I got more. Before the second pour, I taped the heck out of the mold.
I filled the mold, and let it sit overnight.
While I let the concrete set, I got to work on building the mold for the plastic. It took many hours.
It’s a hollow cavity inside. It didn’t fit perfectly, but I made it fit.
I covered the inside of the mold with packing tape, as in my experience, the cast plastic doesn’t stick to it. I tried to reinforce the seams, with partial success.
It leaked out a bit, but when combined, the resin plastic is only liquid for 3 minutes. It gets really, really hot, then it turns white and continues to be really hot for about an hour, even though it cures in just about 10 minutes.
Demolded
I took the molds off both the concrete and the plastic. I can’t say I’m excited about the results. Had the first mold held up, the concrete would look really nice in the front. It had to be the front that gave out. It still reeks of WD-40, so I’m going to take it outside and wash it. That’ll also help to get the cardboard off the bottom that I couldn’t get. The plastic one is slightly better, at least it’s the right shape. The surface finish is wrinkly.
Complaining aside, I’m really pleased that the parts fit together! I’m gonna keep working on it, and get the electronics working. I updated my RedBoard, so it should be ready to mess around with now. I’ll need to buy some tube, but other than that, I’m pretty sure I’ve got all my components. When the rest of the cardboard is cleaned off, I’ll seal the concrete with silicone. I got a tube of pure silicone, and some plastic tools to spread it around.
To anyone who reads this: any ideas about how to finish the surface of the concrete? I was gonna leave it bare, but it’s kinda not nice looking.
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This looked like quite the process to get done, but it looks like it turned out well! I’m glad that no disasters happened with the WD 40 dissolving the adhesive and the plastic form works! I hope you are planning on painting it. (And I’ll keep in mind to not touch concrete for the sake of healthy skin haha)
Nice work! Getting a nice surface finish will be difficult unless you have a power tool used for sanding floors, but those things are humongous. They might have handheld ones but $$$. The only recommendation I have is to grab some more concrete and cover the outside again but this time using a large putty knife to get a nice flat surface. This might be more work than you need to do however. Will you be keeping the plastic piece the same color? Just an idea, you can cover the top piece with veneer wood, it would mesh nicely with the concrete.
Sorry to hear you struggled so much with this process, but you kept at it and adapted, which is impressive. I have not read you previous updates so I am not sure exactly what you are making or what aesthetic you are going for, but as potential ideas, you could cover the concrete with a veneer wood or spray-paint it. You could do a solid color or a design (potential for great creativity here).