Tips and Advice

Q:

Honey-combing is caused by a number of different reasons which are:

• Insufficient compacting or vibrating
• Segregation of the concrete when it is allowed to free fall from heights over three feet.
• When the steel reinforcement is too close to the formwork (boxing).
• When the formwork is not nailed tight and the grout from the concrete leaks out.
• When too stiff a concrete is used without the proper vibrating equipment.

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 place 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 a few hours after being placed, and the deeper the section the greater the settlement will be, settlement cracks occur over beams mainly.

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.