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1950-51 Theatre Catalog, 9th Edition, Page 130 (110)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 130
Page 130

1950-51 Theatre Catalog, 9th Edition, Page 130

is made to meet standard specifications. It should be protected from moisture while in storage to prevent deterioration. Water used for mixing should be clean. Clean, hard, tough, suitably graded aggregates give more wear-resistant concrete than materials which are inferior in these respects.

The less water used in mixing concrete, the stronger, more wear-resistant and more watertight it will be, provided the concrete can be placed properly.

For uniform concrete, a mixture that does not permit segregation of the ingredients must be used. The proportions of the various sizes of aggregate and aggregate to cement and water should therefore be such as to prevent their separation during handling and placing.

The chemical combination of cement and water to produce hard, strong concrete requires time. During this time moisture must be available, either by preventing evaporation of the water used in mixing or by replacing that which does evaporate.

Applying these basic principles to concrete fioor finishes, the following requirements should be observed:

1. Use only suitable materials.

2. Use not more than 41/2 to 5 gal. of

mixing water per sack of cement. This includes water introduced as surface moisture on the aggregates.

3. Use mixtures and construction methods which will not permit segregation resulting in free water and fine material on the top surface. A

4. Prevent early evaporation of water by keeping the concrete wet as long as practicable.

The aggregates constitute such a large proportion of the concrete volume and have so much infiuence in producing wear-resistance that they are of first importance.

Aggregates for Floor FinisheSince the aggregates in the wearing course are subject to abrasion, they should be of sufficient toughness and hardness to resist that abrasion. Where conditions are severe, traprock of a dense, finegrained and interlocking crystalline structure or hard, fine-grained granites and quartzites are excellent. Where the duty impOSed is not so severe, such as floors of a decorative nature, aggregates of less hardness may be selected.

Aggregates may be either gravel or crushed stone. Materials containing a large proportion of elongated or thin fragments should never be used. All aggregates should be clean, free from dust or highly weathered fragments and should consist of particles which will not alter in physical or chemical nature in the presence of moisture. New and untried aggregates should be subjected to study before they are used in finishes intended for long service under severe conditions.

The economy of properly proportioned and correctly constructed concrete floors is lost if weak mortar toppings are used. In a correctly built concrete theatre fioor, tough, hard, durable aggregates are firmly held in a portland cement paste of high strength. These aggregate particles are at and near the surface of the fioor, and are the wear-resistant constituent of the concrete. Since the aggregates perform this important duty and represent about three-fourths of the mass of the hardened concrete, the necessity for proper quality can be readily appreciated.

Cement and sand mortar toppings should never be used for heavy-duty floors such as those in theatres, and, for that matter, should be avoided even for light traffic. There are no large particles of durable aggregate in a weak mortar

topping to resist wear. Mortar toppings

also shrink more, and thus are more apt to crack or craze. Since it is made of fine material only, a mortar topping works

THE SPECIAL PROBLEMS OF AUDITORIUM FLOORS are considered in the accompanying diagram. Once the structural base slab has been properly leveled and compacted, the.msles should be located and the carpet strips and grounds installed to proper floor slope. Latter promde screeds for floor and aisle and protection of carpet depression edge until curing. Note wearing course to accommodate chair bolts.

easily and a very smooth finish can be produced. For this reason, it has been all too commonly used without thought as to its performance.

Mixes for Floor Finish-The amount of mixing water should not exceed 41/2 to 5 gal. per 94-lb. sack of cement. The amount of surface moisture in the aggregates should be carefully determined and this amount subtracted from that specified. The exact proportions of the aggregates will vary somewhat with their gradings and are best determined by trial.

Job experience and tests have proved that the wearing quality of a concrete floor is to a great degree influenced by the proportions of cement, sand, and coarse aggregate, plus the proper amount of clean mixing water. A concrete floor finish made with a large percentage of sand as compared with the quantity of coarse aggregate will not be durable.

The most satisfactory mixture for durability is one made of 1 part cement, 1 part sand, and 2 parts of coarse aggregate. The coarse aggregate should be graded from 1A; to % in.

Workability of Concrete a Concrete should be of such proportions and have such workability that it can be compacted and each aggregate particle becomes completely surrounded by cementwater paste, leaving no honeycomb nor voids. Floor topping is laid in a relatively thin layer and is compacted by tamping, rolling, fioating, and troweling. Therefore, a stiff mixture can be used. Stiff mixtures are advantageous, as they permit less mixing water and more aggregate with a given amount of cement and prevent segregation of the materials. Such concrete is best mixed in the open top paddle type mixer.

It is desirable to have as much as possible of the coarse aggregate near the surface of the floor to take the abrasion and wear of service. An excess of fine aggregate should, therefore, be avoided as it tends to work to the surface during compaction, thus defeating the purpose of the coarse material. On the other hand, the mix should not be too harsh for the methods of construction used. Harshness should be corrected by adjustment of the proportions of fine and coarse aggregate and the total amount of aggregate. The specified amount of mixing water should not be increased to produce workability.

Thickness of Finish - The wearing finish of concrete floors should be not less than 1 in. thick, whether it is placed at the same time as the structural slab or after the concrete in the structural slab has hardened. The thickness of structural slab will, of course, depend on design requirements. As pointed out previously, the finish on auditorium fioors must be at least 2" thick to provide for 1%" chair anchor bolts.

When fioors are placed over a membrane waterproofing or over insulation, a reinforced slab at least 3 in. thick should be placed over the membrane or insulation. The top 1 in. may constitute the wearing finish,

Importance of CuringeThe chemical reactions between cement and water which cause it to harden continue indefinitely if moisture is present and

1950-51 Theatre Catalog, 9th Edition, Page 130