We worked with aluminium foil in free form. We needed to add an additional 200 g of water for the concrete mix to flow easily and get down to the bottom. The aggregate we used for the inside of the aluminium shape was perhaps to small, so the concrete didn’t get down in a good way. If we were to do it agin, we would use larger aggregate so that we wouldn’t have to use so much water.
The shape after we took it out of the form after 24 hours. There was some leakage on the top, but that rather made it more interesting. Overall the shape was kept intact.