Machine Cast Sheet
Machine-cast or DM (Direct Method) Lead sheet was developed as a building material in the mid 1950s in Australia and introduced into the UK in the 1980s.
It should not be confused with either rolled sheet or traditional sand-cast sheet.
It is produced by immersing a rotating water cooled metal drum into a bath of molten lead, the lead solidifies on the surface of the drum and is lifted from the molten bath and is peeled away as the drum rotates.
The thickness of the sheet produced is determined by the speed of the drum rotation, the depth of the immersion and the temperature variation between drum and bath.
Machine cast sheet differs from rolled and sand-cast sheet in both surface finish and grain structure. The surface of the finished sheet not in contact with the drum has a dimpled finish whilst the other side is comparatively smooth.
Machine cast sheet is not made to a British and European Standard and cannot be consistently produced in the UK to the thickness tolerances achieved by rolled sheet.
Individual DM manufacturers in the UK have obtained their own British Board of Agrément Certificates but these only detail the chemical, physical and technical characteristics of each manufacturer’s own product.