284 AROUND THE YEAR IN THE GARDEN 



fracture will be found to run through the stones. It is 

 practically solid rock. 



The proportions of the ingredients are varied according 

 to the nature of the work for which the concrete is to be 

 used. There are three standard formulas, known respec- 

 tively as "lean," "medium" and "rich" mixtures. The 

 former is used for thick retaining walls, floors, sub-bases 

 and anywhere where bulk and weight, rather than strength, 

 are required. A medium mixture is used for ordinary pur- 

 poses, such as walks, curbs, steps, walls, etc., and a rich 

 mixture where great strength, fine finish or imperviousness 

 to moisture are needed, such as for more elaborate forms of 

 walls, garden furniture, supporting posts, thin walls, etc. 

 "Reinforced" concrete is simply concrete with some mate- 

 rial, usually metal in the shape of wires, rods or woven-wire 

 netting, to give it extra strength for such uses as complicated 

 forms, thin walls, floors, and anywhere where special stress 

 and strain may be encountered. 



The proportions for these several mixtures are usually as 

 follows, though, of course, they may be varied after one has 

 a little experience, as the requirements of the job suggest: 



Lean mixture: One part cement; three parts sand; six 

 parts gravel. 



Medium mixture: One cement; two and one-half sand; 

 five gravel. 



Rich mixture: One cement; two sand; four gravel. 



Finishing mixture: Three shovelsful of clean, sharp sand 

 to ten pounds of cement. 



The latter mixture is used for finishing off curbs and 

 gutters, surfacing walks or walls, etc. It should always be 

 applied before the first form has set hard. 



After the materials are got together, and you know 

 exactly what you want to construct, the forms must be 

 prepared. For most work they are made of wood. The 

 "form" is simply a casing to hold the wet cement in shape 

 until it hardens. For any job that requires considerable 

 'concrete, the forms are generally made in sectional units, 

 which can be used over and over. In making up the forms, 



