An embossed sheet, on which fine embossed patterns are regularly formed on a surface, is manufactured without any defects and with a high quality at a high line speed and at a high level of productivity. The assembly includes a float and a weir opening that is in fluid communication with an outlet from the vessel. The waterproofing membrane composition contains a flexible polymer, preferably an epoxy containing polyether chains formed from a glycol, a flexible curing agent, sand, and an aramid fiber. Then, the raw material substrate is cut to form a grid-shaped substrate having a plurality of strip-shaped structural parts.