Surface cracks can be of two types ‘shrinkage’ and ‘settlement’ cracks.

Shrinkage Cracks: These are short semi-circular cracks which appear on a slab when the surface of the freshly placed concrete is allowed to dry. When the surface becomes dry, stresses build up within the concrete. These stresses subject the concrete to tensile forces, and since concrete is very weak in tensile strength, the concrete cracks. The pattern of cracking is very irregular.

Settlement Cracks: These are cracks which occur directly over deep sections of concrete. They usually adopt a pattern similar to that of the reinforcement directly under it. Since all concrete settles within few hours after being placed, the deeper the section the greater the settlement will be therefore, settlement cracks occur mainly over beams.

Both types of cracking are influenced by additional water in the concrete, improper curing, improper placing, insufficient compaction. Shrinkage cracks are also influenced by high winds, direct sunlight, hot and humid weather, which all speed up the drying of the surface of freshly placed concrete.