z86 FLOORS 



was filled in, then five inches of concrete made of coarse gravel, coal- 

 tar and pitch, and finally about one inch of fine gravel tar concrete. 

 Before the concrete was laid, heavy stakes were driven about three feet 

 apart to which the 4" x 4" floor timbers were nailed and leveled up. 

 The concrete was then filled in around the floor timbers and thoroughly 

 tamped. A layer of hot coal-tar was then spread on top of the concrete 

 and the flooring was laid and nailed to the timbers. It is very es- 

 sential that the gravel be perfectly dry before mixing and this is ac- 

 complished by mixing it with hot coal-tar. What is known as dis- 

 tilled or refined coal-tar must be used as that which comes from the 

 gas house without being refined does not work in a very satisfactory 

 manner." 



The following paragraph is abstracted from Report No. V., Insur- 

 ance Engineering Experiment Station, Boston, Mass : 



"Floors over an air space or on cement are subject to a dry rot. 

 Asphalt or coal-tar concrete is softened by oil, and the dust will wear 

 machinery unless the concrete is covered by plank flooring. Floors 

 made by laying sleepers on 6 inches of pebbles, tarred when hot, then 

 2 inches tarred sand packed flush with the top of the sleepers, and cov- 

 ered with a double flooring, have remained sound for 37 years. Double 

 flooring at right angles can be laid on concrete without the use of 

 sleepers. It is usually preferable to secure nailing strips to stakes 4 

 feet apart each way and driven to grade, concrete flush to top of strips, 

 and lay i^-inch flooring." 



The floor shown in Fig. 135 was laid in an extensive shop on the 

 Boston & Maine Railway. The earth was well compacted and brought 

 to a proper surface and a 4-inch bed of coal-tar concrete put down in 



?/ 



Roofing Pitch 

 *"* Compacted Earth 



FIG. 135. 



