I have been experimenting with different types of plaster here. I get the material in a shop called Riesco off Gran Via in the centre of Madrid.The materials are cheap and there is a good selection but you have to experiment to find out what you want to achieve. These aeroplanes are made using Escayola exaduro (2 kilo to a plane mould) this is about twice the normal amount of plaster you would use.The escayola set really hard and strong (feurte) , you still would not want to drop it though!