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250 RICHARDSON'S BLUEBOOK OF PROJECTION
The Floor
(18) The best floor is a top dressing of high grade cement and sharp sand (insist upon the high grade cement and "sharp" sand) laid down not less than one inch thick, supported by a substantial thickness of rich concrete of cement, sand and medium-size crushed stone well tamped into place, with all the various projector and other necessary anchor bolts, conduit, etc., embedded therein. (19) The concrete underlay should be of sufficient thickness to be impervious to vibration set up by the machinery. Be guided by the architect on this point, though a six-inch thickness should be quite sufficient.
(20) Unless the floor is to be painted or covered with linoleum or other material, it is imperative that only high grade cement be used for top dressing. Poor quality cement will be scuffed up rapidly into dust, which will settle on the film, causing minute scratches, get into the machinery bearings causing them to wear very fast, get into the sound equipment causing noisy sound. The best cement will do this to some extent, but a poor quality deteriorates quite rapidly.
(21) Under no circumstances is it good practice to use a floor of raw cement in a projection room. (22) The best covering is "battleship linoleum," dark green or brown in color, cemented to the floor. (23) If linoleum is too expensive, cover the floor with two coats of paint. There are acid treatments that do fairly well in preventing dust formation, but paint is more reliable, and linoleum the best.
Dimensions of Room
(24) Under no condition should the ceiling be less than eight feet from the floor in cool climates. It should be twelve feet in warm climates. The higher the ceiling the better.
(25) The length of the room is dependent upon the number of projectors and other equipment it has — such as spots, effect projectors, stereopticons, etc. Starting