When mixing the fabric-concrete, we needed to add an additional 290 g of water to a 1 kg mix in order for the concrete to flow easily.
We used the non-strechty fabric and placed nails on a board underneath the fabric. When adding the concrete, the load of the concrete hopefully creates a flowy landscape around the pikes of the nails.
Varying stretch 10×20.
We placed a non-stretchy fabric around a frame, made some holes and then added the strechty fabric on top. The weight of the concrete should then make deeper “valleys” of concrete where the holes in the non-stretchy fabric are.