1st. The materials must be perfectly clean.
2d. The mixing must be in proportions carefully determined.
3d. The mixture must be used while absolutely fresh.
Good results cannot be obtained unless you use a good cement, nor will
the work be at its best unless care is taken in the selection of clean
sand and clean stone.
Among the uninitiated, there is an all too prevalent idea that anything
is good enough for the making of concrete. Some will tell you that
sawdust, shavings, mud, clay, etc., will do to complete the mixture,
but the absurdity of this notion will very soon become evident to
anyone who neglects the precautions which have been above pointed out.