286. Weight and Strength

The weight of terra cotta in solid blocks averages 122 pounds per cubic foot. When made in hollow blocks 1½ inches thick the weight varies from 65 to 85 pounds per cubic foot, the smaller pieces weighing the most. For pieces 12x18 inches or larger on the face, 70 pounds per cubic foot should be a fair average

The crushing strength of terra cotta blocks in 2-inch cubes varies from 5,000 to 7,000 pounds per square inch.

Hollow blocks of terra cotta unfilled, have sustained 186 tons per cubic foot.

From these and other tests the author would place the safe working strength of terra cotta blocks in the wall at 5 tons per square foot when unfilled and 10 tons per square foot when filled solid with brickwork or concrete

If it is desired to test the strength of special pieces, two or three small pieces should be broken from the blocks and ground to 1-inch cubes, and then tested in a machine. Should the average results fall much below 6,000 pounds the material should be rejected.

287. Protection

The carpenter's specifications, should provide for boxing all moulded and ornamental work with rough pine boards to guard against damage during construction. Hemlock is unsuited for this purpose as it is liable to stain the terra cotta.