... available are 12.5 mm (modern equivalent of half an inch), typically used for walls, and 9.5 ... mm (modern equivalent of three-eights of an inch), typically used for ceilings. 15 mm thick ... , and plain edge, used where the whole surface will receive a thin coating (skim coat) of finishing plaster. ... doorway.As opposed to a weeklong plaster application, an entire house can be drywalled in one or two ...