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Mold Making? Answered

So, after making this awesome isntructable (it's curing now!), I got ideas for other concrete projects. My favorite so far is making a concrete lamp. I want to make a mold of a lamp (light bulb in it) and then cast it in concrete. I'd then put a real lampshade on it and call it art. My problem is...I have no mold making experience. Do you guys have any tips, know where to get silicone, etc?




9 years ago

Hi, I'm actually writting an instructables about how to make a lamp with concrete, optic fiber, and leds. It won't help you with molding, but maybe we can share ideas / reviews. Just send a message if you want.

Plaster of paris is my favorite for small-to-medium molds. I'm not sure if I'd use it for a lamp, though. Using your mortar mix might work, and when it's dry, putting a coat of acrylic and then waxing it would make it easy to use as a casting mold. If you want, you can use RTV gasket material from the auto parts store to make a mold, but bear in mind that this stuff is thicker than the mold-making sort. A little birdie told me you can get the moldmaking sort at most craft stores.

. You may be able to get a glossier finish by powdering the inside of the mold with concrete dust before pouring. . You should be able to find silicone grease/spray/&c; at most industrial electrical/electronic outlets.

They use a lot of silicone in make-up effects etc - try a local theatrical suppliers.

Online, try looking for alginate - like this stuff (that's just an example, not a specific recommendation).

There's more information here and this company seems quite relevant as well.

Oh! That last link offers free shipping and reduced prices for first-time buyers in the US. (link)

Hmm, the website seems to only sell in bulk, unless I'm missing something. That, or prices in the $500's are normal.

Ah, well. At least it gives you something to look for. Unless you can talk a sample out of them?

To make the mold? I really don't know - mold-making is not something I've tried before. I guess, though, that if I wasn't using a flexible mold (like the silicone), I would use plaster or paris - push the lamp halfway down into a bowl of it, sideways, and leave it to set. Lift the lamp out and repeat for the other side, then press the two halves together to make the negative to cast the concrete. I guess.

DO NOT use plaster of paris, I was making this awesome project once with electronics embedded in resin, and I made my mold out of plaster of paris, it cracks and crumbles and it's just bad news

You should try adding a bit of PVA to the mixture, it worked for me. Although as for a disposable mold I would use wax.