An apparatus for mounting and demounting a materials sheet onto and from a cylindrical surface of a drum (10) has clamps (40) pivotably arranged upon the sheet materials drum. The clamps have a first region (80) and a second region (70) either side of a pivot axis. The second region (70) clamps the materials sheet to the cylindrical surface (20) of the drum. A backbone (120) extends along the length of the drum and is removably attached to the drum. Push rods (90) movably arranged on the backbone are capable of being operated to push against the first region of the clamps to pivot the clamps to move the second region of the clamps. Any existing clasped materials sheet is thereby unclasped from the cylindrical surface.