1kg of dry PTP covers approx. 30cm x 30cm x 6mm thick/20kg bag of dry PTP covers 3 square m x 13mm thick.
Premium is most effective as a strong hollow shell. This saves both time, effort and money.
Build a supporting core first (Foil, foam, wire, etc).
Over this, apply a thin coat of Premium and begin sculpting. Coating thickness is dependent on size: Small sculptures need 3mm
Mid-sized pieces need 4-6mm. Larger work needs 20mm