#45951, "RE: modelling the ocean floor for a wreck model" In response to In response to 16
The easiest thing is Plaster of Paris from any home improvement store. I stapled down loosely some nylon screen like for a screen door first. After the plaser sets up, use wood working to tools to carve shapes and sand it to the surface you want. Do that OUTDOORS. The dust is awful.
Modeling clay comes from an arts and crafts store or possibly floral shop. It takes days to dry. It shrinks when it dries and can curl if applied too thin. It's a lot more expensive. Not recommended for this.
Model filler putty can be added anywhere on the plaster for small touches. Anything you use needs to be painted.