A quick step-by-step guide showing how I made a hill on the corner of my Selly Oak project.
The basis of the hill is expanded polystyrene blocks fixed together with PVA glue and then carved to shape. Ideally, you do this with a hot wire cutter, but a less smelly, if considerably messier, method is to use a bread knife.
To give the hill a hard shell, pieces of plaster impregnated bandage, often sold under the trade name Mod-Roc, are dipped in water and then laid on the hill. By overlapping them and then smearing around the wet plaster with your fingers (another messy job) the whole hill is covered and left to dry overnight.
I like quite a thick "crust" on my hills and while I could achieve this with extra layers of the plaster bandage, using some DIY store wall filler is cheaper. Apply it with a palette knife or one of these spatulas used for icing cakes. Wet the tool as you work, it makes the filler go on a lot smoother.
Once the hill is covered to 2-3mm, leave it to dry overnight.
You might be better at plastering than I am, but generally, the surface needs sanding to get it smooth.
We're not looking for perfection, just to take the worst lumps and bumps out of the surface. Imagine you are a scale person standing on it and then think about a real hill. They might have the odd crevasse or cliff edge, but generally the land is smooth thanks to years of weather and erosion.
This is another messy job. Have a vacuum cleaner to hand and use it constantly. You really don't want this stuff in your pointwork.