Thread: Concrete in plastic mold

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If I pour mixed concrete into a plastic tupperware form, something maybe round 16" in diameter, and maybe 3 inches thick, will I be able to easily remove it from the plastic container, or will it bond to the plastic? I will have a piece of wood sticking out of the middle as it hardens, so this could help pull it out. Didn't know if any kind of releasing agents would help or if it was even needed.

I'm not a concrete specialist and have never used it, but it seems like if you used a cheap throw away plastic container that you could probably just break it off when its set? Just an idea.

Concrete won't stick to plastic.

They use to make the lids for septic tanks this way. They would take a plastic bucket, set it in the form and add a rebar handle. Then pour concrete around the bucket and in the bucket. When dry they will lift out.

Originally Posted by MsMeeple

I'm not a concrete specialist and have never used it, but it seems like if you used a cheap throw away plastic container that you could probably just break it off when its set? Just an idea.

I wanted to reuse the container rather than having to buy several.

I would coat the bowl with vaseline

as long as the bowl does not have straight side or ridges to trap the concrete it should pop out

Make a mold release of 1 part dish washing soap to 1 part rubbing alcohol. This will wash right off your casting. Vaseline will be harder to remove and cause trouble if your going to paint the concrete.

Also consider the first rule of mold making and casting. If you casting is going to be hard, use a soft mold, if your casting is soft use a hard mold. If the mold and the casting are both hard, they will mechanically bond together like puzzle pieces. Only the most simple molds will work hard and hard.