TERRAZZO: One specimen was of monolithic terrazzo, i.e., the terrazzo was placed on the base slab a few hours after the base slab was cast but before the base slab had hardened. No ties were used between the two courses. Two specimens were of sand cushion terrazzo, i.e, the underbed was isolated from the base slab by a layer of sand 1/4 inch (6mm) thick, and a layer of building paper. The sand cushion terrazzo specimens were cast within sheet metal side frames and were kept in a horizontal position to prevent disturbance of the sand layer. Except for the monolithic terrazzo, the base slabs were cured 5 days under damp burlap before the underbed and terrazzo were applied. The underbed consisted of one part cement and about 4-1/2 parts sand (by dry loose volume) with just enough water to permit molding. The underbed was tamped into place and several different types of divider strips (brass, white metal, and plastic) were used. Various colors of 1/4 to 3/8 inch (6 to 10 mm) marble chips were used in the terrazzo. One day after placement, the terrazzo was ground, but not polished. All terrazzo work was done by qualified terrazzo mechanics.

Two additional specimens were cast entirely of the underbed mixture.

Terrazzo floor data is shown in the chart below. In each of the tests of terrazzo floors, the average temperature rise of the unexposed surface of 250 degrees F (139C) governed, even though two thermo-couples were located over divider strips. The fire endurance of the 5 inch (12.7 cm) monolithic terrazzo specimen was about the same as that of a 5 inch (12.7 cm) single-course slab. Two specimens of bonded terrazzo had endurance periods 16 and 24 minutes longer than single course specimens of the same total thickness. The sand cushion terrazzo specimens had endurance periods more than 1 hour longer than single course slabs of the same total thickness.