OIL-MIXED PORTLAND CEMENT CONCRETE. 13 



For waterproofing cisterns, oil-mixed concrete will prove of great 

 benefit. It is absolutely necessary that cisterns which are buried in 

 the ground be waterproofed to prevent contaminated ground water 

 from seeping in, as well as to prevent the cistern water from escaping. 

 Buried cisterns of rectangular shape should be reinforced to resist 

 the earth pressure, which tends to bulge the side walls inward when 

 the water runs low. The reinforcement should, therefore, be pro- 

 vided on the inside or tension side of the walls. The earth pressure 

 will prevent the tank from cracking when it is full of water. 



For cistern construction a mixture composed of 1 part of cement, 

 2 parts of sand, and 4 parts of gravel or broken stone, together with 

 10 per cent of oil, is effective. The inner faces of the cistern should 

 be painted with an oil-mixed cement grout applied with a stiff brush 

 and rubbed well into the face of the wall. Two coats of this grout, 

 containing about 3 per cent of oil, should be used. 



Barns constructed of concrete are gradually coming into use because 

 of their durability, cleanliness, resistance to fire, and economy. It is 

 essential that the interior of these structures be kept free from mois- 

 ture, and for this reason it is well to waterproof the concrete mixture 

 entering the side walls and flooring. The side walls, unless water- 

 proofed, have a tendency during a long beating rain to absorb and 

 retain much moisture, and this moisture penetrates to the interior. 



If oil in amount equal to 5 per cent of the weight of cement be 

 mixed with the concrete used in the side walls, this damp condition 

 of the interior becomes impossible, because the admixture of oil pre- 

 vents the penetration of the moisture. 



Barn floors should be waterproofed by the addition of oil as pre- 

 viously described. A damp-proof floor has the advantage of remain- 

 ing dry and hence warmer, because there is no evaporation from the 

 surface. It is likewise more sanitary than an ordinary concrete 

 floor because of its nonabsorbent character. 



CONCRETE BLOCKS. 



The use of concrete blocks in the building trade is yearly increasing. 

 Much criticism has been heaped on the building block, and in many 

 cases the criticism has been just. It is recognized that many con- 

 crete-block houses are damp, owing to the fact that the walls are 

 very porous and absorb and retain much moisture after a heavy, 

 beating rain. A building block generally need not be waterproofed 

 against water pressure, but it should, however, be rendered proof 

 against the permeation of water by absorption. The use of a small 

 quantity of mineral oil in a concrete block renders it extremely non- 



