The crown will be about 9 or 10 cm thick. The lower 8 centimeters is steel-reinforced concrete. This is capped by a 1 cm layer of self-levelling poured screed. This is a non-viscous, fiber-reinforced cement that flows to a level surface.
It is a simple task to make the formwork for the crown. Sub-roofing panels (commonly used underneath ceramic roofing tiles) are flexible, thin fiberboard that are waterproof on one side. These are easily fastened to the expanded clay aggregate blocks with wood screws drilled through wooden stiffening ribs (see photos below).