8 July, 1907.] Use of Concrete for Silos. 405 



With local brands of cement, "air-slacking" is of great importance. 

 If at all possible, the cement should be emptied out on the floor of some 

 building, sound enough to protect it from the wind and weather. It 

 should so remain about three weeks and should be turned over twice in 

 that time. With the imported brands, sufficient time to insure effective 

 " air-slacking " has elapsed since their manufacture, 



" Rendering," by plastering the rough outside surfaces of the concrete 

 with cement and sand, is not to be recommended. It is difficult under 

 the best of circurnstances to make a good job of it, and unless well done 

 it is better left alone. If a specially smooth surface be desired, it can 

 readily be attained by making a facing of cement mortar put into position 

 as the filling with the ordinary concrete progresses. Special moulds, to 

 be draw^n out as the filling progresses, may be employed ; but the shovel 

 is sufficient for all practical purposes. 



In this State little use has as yet been made of concrete for buildings 

 save for foundations and for some instances of reinforced concrete, that 

 is, concrete with steel bars or rods built in with it to increase its tensional 

 strength. The Hodlow Concrete Wall Company of Melbourne has lately 

 introduced a method of constructing buildings with concrete blocks which 

 has much in its favour. The walls resulting from its system are hollow, 

 though solid blocks, not hodlow as in some of the American systems, are 

 used. Reference to the illustrations will aid in following the ensuing 

 descriptions. 



By means of a moulding machine, the patent rights of which are 

 held by the companv and which can be obtained on hire at reasonable 

 rates, blocks of 24 inches in length and 12 inches in breadth are made, 

 the thickness being under the control of the operator. Running across 

 the width of the block and in a central position is a projection called a 

 '' root," which is from 3 to 4 inches wide and of a depth depending upon 

 the thickness of the wall to be constructed. The block is T shaped in 

 section. For ordinarv 9-inch walls, the thickness of the block is about 

 ih inches and the " root " projects about 5 inches. Concrete is mixed as 

 described above, a sufficient quantity put into the machine and the block 

 moulded. It is then lifted out on a "bearing oft"" board and put aside 

 until set sufficiently to handle in building. This takes a few days, 

 depending upon the weather and the brand of cement used. During this 

 time, the blocks should be kept well damped. One man with the assist- 

 ance of a lad can make from 100 to 150 blocks in a day, equal in a 9-inch 

 wall to 1,000 to 1,500 ordinary bricks. One cask of cement, and one 

 cubic yard of gravel and sand will make about 80 blocks. A man with 

 the same assistance will, after a little practice, lay 100 blocks per day ; 

 that is, a wall 10 feet by 10 feet high. Special blocks may be made for 

 corners, door jambs, &c. The blocks are set in cement mortar of suitable 

 strength in a double row wdth the '' roots " alternately opposite the joints 

 between the ends of the opposite blocks. In the next row or course, the 

 blocks break joint and consequently the " roots " come on top of one 

 another from either side, making the work complete and satisfactory vet 

 allowing the free circulation of air throughout the interior of the wall. 



As an experiment to test the cost and the strength of such a method 

 of construction for silos, one was erected at the Ballarat Orphan Asylum. 

 This silo with its novel appearance, added a new interest toi a pla,ce 

 always attractive by its charming flower beds, its well-kept kitchen 

 garden, its neat, well-drained and cultivated paddocks, and last but 

 not least, well-trained and happy-looking inmates. The silo was erected 



