Timber Split And Crack Preventative Treatment Supro Em.is a ready-for-use wax emulsion that is compatible with and effectively seals green (freshly cut) timber, particularly the end grain. Upon drying it forms a water resistant coating that prevents excessive checking and end splitting during drying of the timber. SUPRO EM also acts as a highly effective water repellent sealer. It has a milky white appearance and dries to a translucent coating. SUPRO EM is also available with colour additives for visual identification.