ARTIFICIAL STONE, OR CONCRETE 



to the concrete block. Besides this, the concrete 

 block is stronger and more resistant to moisture, at- 

 mospheric conditions, and fire. These qualities, to- 

 gether with the flexibility of concrete as a working 

 medium, give concrete blocks the position they now 

 hold as building material. 



Although the concrete block, when finished, has 

 such remarkable qualities, there is nothing complex 

 or extraordinary in the process of its manufacture. 

 Any person with reasonable intelligence, a little knowl- 

 edge, and sufficient industry to see that the com- 

 ponent materials are well mixed, can make a first class 

 article of concrete. The exact proportions of the 

 materials are less essential than the thorough mixing 

 of them. Thus, one part Portland cement, two parts of 

 sand, and four parts of gravel, or broken rock, when 

 thoroughly mixed with water, will set into a good 

 concrete block; the more thorough the mixing the better 

 the block. The exact amount of the hard sub- 

 stances, and the amount of water used, may be varied 

 within wide limits; but there is no deviation from the 

 cardinal rule of thorough mixing. "Ultimate success 

 with any mixture," says one writer, "can only be ob- 

 tained by the entire coating of every grain of sand 

 with cement, and every piece of stone or gravel with 



sand-cement mortar Only by this method 



can voids be eliminated and the greatest strength ob- 

 tained. There are, however, other advantages resulting 

 from an absence of porosity. The permeability of a 

 concrete block is greatly reduced by added density, and 

 with sufficient attention to this matter the question 



