The truth is that cracking is one of our more serious problems, and at least a fair share of the trouble can be attributed to modern construction practices which sacrifice quality for haste. Most cracks, however, can be readily explained and once the cause is understood preventive steps can be taken. T. Boyd Mercer has classified concrete cracks into two broad categories: he includes those that occur before hardening and those that occur after hardening. Sub-types in the before hardening category are constructional movement; settlement shrinkage; and setting shrinkage. After hardening cracks are classified under six headings: physical, chemical, temperature, stress concentrations, structural design and accident. Preventive measures for before hardening cracks are: make sure that the subgrade is properly compacted, make sure formworks don't move, use dense plastic mixes and give more attention to the compaction of the concrete, make sure concrete is retaining enough water, and erecting windbreaks and shading concrete surfaces from the sun in summer. Preventive measures for after hardening cracks are: avoid excessive floating, to throughly cover with concrete all reinforcing steel, make sure there is sufficient concrete over the reinforcing bar, and reinforcing corners of door and windows.