Richardson's handbook of projection (1930)

1238 HANDBOOK OF PROJECTION FOR (c) The material should have as low specific heat as possible to prevent its becoming a "storage reservoir" for heat. (d) In some cases the weight will have to be considered if the building structure supporting the projection room is not amply strong. In this connection your committee desires, without recommendation, to point out that for wall construction hollow tile eight inches or more in thickness set in rich mortar strongly tempered with cement, and covered with a smooth hard finish plaster, fulfills all of the above requirements better than any other material. The floor slab should support the projection equipment without the slightest vibration, and be of a material which will not wear away and form dirt or dust. We therefore recommend that the floor slab be of concrete of approved mixture, not less than six inches thick, covered with an approved top dressing of cement and covered with battleship linoleum or rubber tile firmly cemented to the floor slab. This linoleum or tile should be laid after all plastering, painting, wiring, etcetera, has been completed, but before any of the projection equipment has been installed. Before the projection equipment is installed the linoleum should be thoroughly cleaned and waxed to prevent it absorbing oil from the machinery. Incalculable damage has been done to projection machinery and to sound film by the fine dust rising from uncovered projection room floors; such stone floors belong to the stone age, and have no place in the modern projection room. Aside from their injurious effect upon equipment, they have the effect of unduly fatiguing those who must stand constantly upon them, thus reducing their alertness and lowering their efficiency,