Duraloid Coatplast is a two component tixotropic chemical to make hard polystyrene to apply by brush directly on the polystyrene surface in order to have a protective shell.
After adding the component B into component A mix very well and then apply by brush. Create a layer of 1mm thickness and leave to dry at a temperature of 25°C. Its tixotropic agent allow to apply in vertical without any leankage.
After drying use sandpaper to smooth the surface and then color it as you prefer.