CAUSES OF DEFECTS Frozen concrete surfaces have the appear ance of being spotted. A surface frozen before the concrete has set, scales off easily. Paper, tarpaulin, or clean sand can be used to prevent freezing. Good cement work can be done in freezing weather by using warm water, warm sand, and gravel, and protecting the material from freezing.
have the appearance of over-burned clay. Good results can be secured in hot weather by covering with canvas.
surfaces look streaky when set. Dirty streaks are caused also by the use of unclean materials.
By using too much water in the top mix, the cement is washed out, and a good union between the top and concrete is not obtained. The sur face coat is also prevented from adhering by dirt or by weak concrete.
makes the work porous and weak. The top surface should be laid be fore the under concrete is set.
the surface coat causes hair cracks and work that is slippery, rough, and wavy.
are caused by poor mixing, by too much tamping, by shocks in the early stages of setting, by poor concrete, by walking on scant ling when work is new, by making the blocks too large for the thickness of the work, by roots of trees growing under the walk, or by not cutting work through at joints to allow for expansion.
are caused by improper floating before marking. Rain on the work before the top has set, also causes pock marks.
is caused by insufficient ce ment, poor mixing, or the use of poor material.
causes honeycombed and streaky work, and also is apt to prevent a good bond between the top and base. Insufficient water will affect the strength of the concrete.