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Customizable Concrete Mold

by Ratmax00, published

Customizable Concrete Mold by Ratmax00 Mar 8, 2013


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There are plenty of ABS molds out there but most are made with a very thin layer of ABS that is almost pliable. Giving the mold some more rigidity and breaking it into two pieces would allow us to play with different forms and still be able to remove it easily from it's casing. Let's see what we can come up with!!!

I have been thinking about using Makerbot to make molds for some time now, and I finally got the courage to design something. Now that we have access to customizer, I have so many ideas I can add to this project, so check back for updates as more will be coming. Pictures, additional 3D polygons, letters (raised and indented)...


Have any spare Concrete, Plaster, Paraffin Wax or Mud? If so this may be something you'd like to play with. Have fun with Customizer! FYI - some inspiration came from the website listed below.

Update: Latest molds looking excellent after some light sanding, New pictures uploaded, models curing and soon to be in use. FYI - Insert was removed at hour 2 of drying and the Dodecahedron mold was printed without support.
Update: New version allows text on the model, both embedded and raised.
Update: Pictures uploaded, round two worked better, however the insert needs some troubleshooting, I would suggest taking that out between drying hours 1-4, as this will allow you to take out the insert and still let the mold hold it's shape. round three in the works.
Update: My first attempt at the mold went well but I didn't remove any of the gravel in the concrete and didn't let it set long enough (6hrs). Lessons learned, round two is setting, I'll toss pictures up once I break the mold.

Concrete supplies list:
-- Any single or combination of: clamps, rubber bands, string, a small child that needs something to do... anything that can keep the two mold pieces together for several hours.
-- Super Secret Mold Release Agent (Pam Cooking Spray).
-- Old rag to wipe up the excess mold release agent.
-- The concrete of your choice.
-- A trowel or scoop of some type, to put the concrete into the mold.
-- A bucket to mix the concrete.
-- Some water.
-- A set of pliers if an insert was used.
-- Mesh sieve for removing gravel/rocks from cement.
-- Sand paper/Hand file/Knife - light sanding post mold removal.

Step 1 - Prep your mold:
Clamp your two mold pieces together. This should be clamped as tight as you can as it will remove any tiny gaps (imperfections). Once the mold is clamped you'll have to use some Pam anywhere concrete is going to touch. Yes, my mold had a nice buttery smell to it. You don't have to use much, just a bit. Use the rag to make sure all the corners are well oiled up.

Step 2 - Mix your concrete:
Pretty straight forward. I would recommend removing any large rocks in the concrete by running it through an old mesh sieve (just don't tell your wife). You want to hit about toothpaste consistency when mixing. The concrete should still be able to stand up on it's own but still be well mixed.

Step 3 - Fill your mold:
You can get very creative here. If you have an insert put a bit of concrete in your mold first then place the insert. If you want an equal thickness of cement around your mold, the insert should be level with the top of your mold. Or you can use a dowel, a stick, even your fingers to make an indention into the mold. Add a candle, an upside down hex screw (for a door nob or coat hook), the sky's the limit... or you can just fill it to the top.

Step 4 - Air bubbles:
Lightly tap your mold all the way around, if you're brave you can pick up the clamped mold and tap it on the floor. You want to get all the air bubbles out.... or maybe you don't. if you leave any in there (just a few taps) it gives your mold a unique look. I found using a combination of the insert, covered with a generous amount of mold release agent, and the back of my trowel tapping around the top edge of the mold works great. Don't let your insert float away from you. Hold it in place while you tap until you're satisfied with all the bubbles being out of the mold.

Step 5 - Wait:
How long... it really depends on the thickness of the concrete and the environment where you're letting it sit. I would recommend at least 6-8 hrs before you try to remove the mold. Update: From trial and error I would recommend you take out the insert with some pliers carefully after about 1-4hrs of drying time. Once the cement is rigid, but not so hard you'll not be able to get the insert out or you'll break your cement.

Step 6 - Break open your mold:
Break your mold open with some light jiggling. The previous ones I've created separated extremely well. Once separated, re-prep your mold with some mold release agent and you're set to use it again.

Step 7 - Cleaning:
Use sandpaper, the edge of a desk or a knife to clean up any sharp edges in your final product (concrete). They may not be that sharp now but after a few days they can become dangerous.

Step 8 - Curing (optional):
This is really up to you. I know we still live in an instant gratification society, but if you want something that will last forever, toss the concrete in a plastic bag and let it sit for a few days. Sprinkle it with some water every other day if it's hot out.


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I noticed that you removed the large aggregate rock from the concrete. I believe, if you purchase mortar cement, it is the same just without the large rocks. Just an idea.

I have been trying to design my own molds in PLA, however, I have not been able to make complex forms as they are hard to get out of the mold even though there are no trapping areas.

The molds I've made were all multi-part and I do have some experience with making brick-molds, silicone molds, latex molds and plaster molds.

Would you know of a lubricant that is usable to help loosen the molds from the castings? It's nice to see you also filter your concrete. I hate those little rocks in my concrete. If only there was a commercially available concrete without those pesky rocks in it! (They don't sell it in any supply-store here in the Netherlands).

You might want to get into Pinterest and do a search there for mold releases. There are some specialy for concrete. I recommend trying quickcretes concrete counter top mix for a really smooth sexy looking concrete. No lumps, clumps or rocks with this. More pricey though. They also offer a mold release as well if I am not mistaken. Good luck.

Try a form of cooking spray (PAM) or even carnuba wax may work for you.

Okay, I'll have to try out more, we don't have PAM in the Netherlands, well, haven't seen it here.

I tried corn oil, ptfe spray (tefspray) and bearing grease, but all of them influenced the setting of the concrete.

sorry there are 2 part injection molds , great work , this is it !!!!! make some more yes yes

i hope will see some 2 part injection molds . gtrz eddy

Your Replicator is far, far, too clean, sir.

Hah! I was lucky the build was large enough and the missing/lifted Krylon spots (character) were hidden. The back looks extremely clean, but now the front needs to be vacuumed, as I swept everything forward (just out of reach of the camera). It's like a mini, multi-colored filament, Hoarders episode at the front of my Makerbot.