14 BULLETIN 230, U. S. DEPARTMENT OF AGBICULTURE. 



absorbent, so that even after a hard rain there is no danger from 

 damp walls. In a 1:2:4 mixture, 5 per cent of oil is a sufficient 

 quantity to waterproof properly against absorption. 



Portland cement mortar mixed with mineral oil and reinforced 

 with steel-wire mesh may be advantageously used in the construction 

 of roof slabs. These slabs could be assembled in place on the roof 

 after they have attained sufficient hardness. Reinforced concrete 

 tiles may also be advantageously made with Portland cement con- 

 crete mixed with a small percentage of mineral-oil residuum. 



STUCCO. 



Portland cement stucco is widely used in the construction of many 

 residences. This type of construction is economical, and, moreover, 

 with it many beautiful effects are possible. The term "stucco" is 

 given to the exterior finish coat, which may be applied to brick, stone, 

 concrete, hollow tile, or frame construction. According to the finish 

 desired and the kind of surface to be covered, the stucco is applied 

 in two or three coats. The first, or scratch coat, should be mixed in 

 the proportions of 1 part of Portland cement and 2 parts of clean, 

 coarse sand, with enough water to form a good stiff mortar. If 5 

 per cent of oil is added to this mixture, the scratch coat will be per- 

 manently waterproof. While this coat is still wet, it is roughened 

 with a stick or trowel over the entire surface. The second coat, 

 which may be of the same proportions, is plastered on after the first 

 coat has set sufficiently to support it. The use of oil in this coat may 

 be omitted if desired, and it may be given a rough-cast finish by 

 using a trowel covered with burlap or carpet. 



The second coat may also be applied by throwing it on with a 

 wooden paddle. This produces a rough surface known as a slap- 

 dash finish. A pebble-dash surface may be secured by using a wet 

 mixture composed of 1 part cement and 3 parts pebbles one-fourth 

 inch in diameter. This mixture is thrown on the second coat while 

 it is still soft, and the result is a very pleasing surface. When a 

 pebble-dash finish is used, the second coat, as well as the scratch 

 coat, may be mixed with oil. In most constructions the second 

 coat will be found superfluous, because a sufficiently thick coating is 

 usually obtained from the first application of oil-mixed mortar. 



When stucco is applied to stone or hollow tile, care should always 

 be taken to have the surface well moistened or otherwise a great deal 

 of water will be absorbed from the mortar coat, and so greatly 

 weaken it and cause contraction cracks to form. 



IRRIGATION DITCHES. 



The residts of laboratory tests, previously referred to, which indi- 

 cate that the presence of oil tends to retard very materially the 



