Prevent & Repair Shrinkage Cracking of Concrete
Plastic shrinkage cracking generally occurs in conditions favourable to high evaporation of the surface moisture present in plastic concrete, including high winds, high temperatures and low humidity. Due to the fact that in its semi-fluid state, concrete is unevenly restrained by edge formwork, ground friction, reinforcement and other penetrations, the volume change caused by the loss of water results in cracks in the weaker points of the concrete’s micro structure.
Plastic shrinkage cracking can be reduced - particularly during extremely hot and/or windy conditions - through the application of an evaporative retardant such as MasterKure® 111, which when sprayed onto wet concrete surfaces, creates a protective film that helps to reduce surface moisture evaporation and aids in finishing. Exposed concrete surfaces should be cured using a curing agent such as MasterKure® 250 immediately following final trowelling, thereby further reducing the loss of moisture. The ability of concrete to resist plastic shrinkage cracking can also be significantly improved through the addition of MasterFiber® polypropylene fibres. MasterFiber® fibres will also deliver significant improvements in the performance of both plastic and hardened concrete.
If the cracks are small, it may be best to tolerate them. However, if the cracks are 2mm or greater, and there is concern over watertightness or protection of the reinforcing steel, remedial measures should be taken.
If the area has low traffic, a coating of MasterEmaco® N 5100 will fill the cracks and create a wearing surface. In high traffic areas, coating with MasterTop® 1080 or MasterTop® 1260 may be considered.