Craze cracking of concrete floors is caused by the shrinkage of the cement paste on the surface, and is particularly noticeable when the concrete slabs are damp. But there are certain steps to take to prevent floors displaying this unsightly appearance, says Bryan Perrie, MD of The Concrete Institute.
Perrie says factors the promote crazing of concrete floors include:
• Drying instead of curing before the floor develops much strength, particularly after hard trowelling;
• Curing with water much colder than the concrete, causing thermal shock;
• Alternating wetting and drying at early stages;
• Overusing vibrating screeds and bull floats;
• Overworking and over-trowelling, especially when the surface is wet;
• Floating and trowelling prematurely;
• Dusting dry cement onto the surface before trowelling;
• Using aggregates with excessive clay and dirt; and
• Applying water to the surface during finishing operations.
"Although crazed surfaces are unsightly and may collect dirt, they do not have serious consequences and repairs are seldom necessary. However, grinding the surfaces may be considered when the crazing is shallow and the quality of the concrete is adequate," Perrie added.
For more information, contact The Concrete Institute Information Centre on tel 011 315 0300 or email info@theconcreteinstitute.org.za