75 7 
USEFUL NOTES ABOUT CONCRETE 
HOW TO MAKE CONCRETE.—To 6 parts of sharp 
coarse gravel, rock or other hard metal, put in 2 of sand or 
other gritty material, First form a heap of the coarse 
stuff, then throw sand on top, and cement on that, all in 
the proportions of І of cement to 8 of gravel and sand. 
Commence on one side of the heap and throw it aside 
until it forms another dry heap. Repeat this operation 
until the cement is evenly mixed right through the mass, 
then add water through the rose of a water can, and 
after that give it another turn, mixing thoroughly. 
Mix on boards or flags in quantities, which may be 
conveniently handled, The heap should not be larger 
than can be mixed with absolute unformity, or than can 
be placed in position within an hour afterwards. 
Broken Stone or gravel graded from coarse sand 
up to 2 or 2} inches may be used, in the proportion of г of 
cement to 6 of gravel as stated, but if the gravel is 
appreciably finer, extra cement will be required in pro- 
portion to its fineness. Inside of moulds should be soaped 
to prevent concrete sticking, and when the concrete is 
placed in them, it should be immediately tamped. 
Always keep concrete wet by sprinkling it for 
seven days after setting. If concrete dries quickly it 
cannot be strong. : 
Place concrete as soon after mixing as possible. 
The outside limit is an hour after. Ram sufficiently to 
consolidate the mass, The wetter the concrete, the less 
ramming it requires, When concrete is intended to be 
placed under water, it should never be rammed, but 
should be made extra wet. 
р Too much water for all concrete is better than too 
ittle, 
Materials may be of all sizes from 24 inch cubes 
downwards, Hard angular materials make the strongest 
concrete. 
Earth—especially clay or dirt—in the sand or gravel 
destroys cement. \ 
