Floor construction has been done by grinding in several projects in this country to provide smoother, more maintenance free floor surfaces. In addition, no restriction need be placed on the use of the areas by other trades during the construction period. Two examples will illustrate. In 1942 during the construction of a very large two story housing project in Detroit, the street level floors were all of the locally called "Gibraltar" detail. The thin concrete slabs placed on factory precast beams were screeded substantially level. About a month later, the floor surfaces were ground by terrazzo machines to a smooth and dustproof surface. To obtain a more resistant surface than could be obtained from the concrete mix, dolomite chips had been distributed by hand over the floor as soon as screeding was complete then rolled with a 300 pound roller and rotary troweled. The project included 2,150 apartments in 235 buildings. A similar procedure was used for some 300,000 square feet of exhibition floor space in the New York Coliseum in 1955. There is no doubt at all that this type of finish is less expensive than a later applied industrial finish. The floors are dustproof and extremely hard and give good traction to the vehicles using them. For more elegant work, a second honing of the surface can be done at little extra cost. Most of the areas look very much like terrazzo but, of course, harder. In 1955, the cost of grinding was 13 cents per square foot plus the cost of supervision. Cement finishers handled the heavy terrazzo machines and received $3.85 per hour. Each machine was fitted with nine mushroom plugs of Carborundum. Machines produced form 390 to 520 square feet per day and 19 machines were used. The labor required was one finisher per machine and a laborer who served up t four machines cleaning away the slurry. Edges and borders were finished with a single unit by hand.