Hello,
I would like to make a few disks of concrete; roughly 45cm in diameter / 5cm thick (but also smaller diameters). So far, I have done this by taking an appropriate sheet of metal, bend it into a circle, support it on a wooden board, and covering everything with some plastic (from a plastic bag). The sheet has to be pressed down onto the board with quite a bit of force (using screws) to avoid the wet concrete spilling below it / pushing it up.
Needless to say, this process is inaccurate, messy and not very fun at all. The plastic will wrinkle and the finished product is then looking quite ugly.
I would like to be able to do it with a good end product (smooth surfaces), easily repeated (i.e., the end product should come out of the mold easily without damaging it, there should be little time spent cleaning up and being ready for the next cast), and with as little effort as possible for making the mold. Needless to say, this is for a hobby/fun project, and cost should not be high.
Do you have any ideas? Is there a material that's easily bent into shape but still stiff enough to hold the weight of the concrete (about 15-20kg), can be glued (etc.) to a floor of the same material, and will easily let go of the concrete after it hardens? Something that's available in your average home depot would be best.
Thanks in advance for any wild speculations. ;)