CONCRETING TIP: How to minimise chances of early cracking
Most concrete shrinks while it sets, cures and gains strength. This is because water in the mix rises to the surface and evaporates – therefore the concrete is losing volume.
Shrinkage can cause unsightly cracking. Slabs, driveways and footpaths are vulnerable as these have large exposed surfaces which maximise water evaporation during setting.
When concreting in dry, hot weather, when it is windy or the humidity is low, it is important to prevent early loss of water from the concrete.
Hot days, wind and low humidity in combination or separately can cause these cracks and reduce your working time.
In these conditions, it is important to take precautions when handling, placing, compacting, finishing and curing concrete. This is very important during the spring and summer months, but it can happen at any time of year.
Check the forecast
Avoid concreting in conditions with extreme evaporation rates. The CCAA Smart Concreting App is a great tool for assessing local conditions.
Prepare the ground
Thoroughly dampen the area where you are placing concrete or use plastic sheeting to prevent loss of water.
Place it quickly
Ensure adequate labour and equipment is available to place the concrete as soon as possible.
Vibrating is essential for compacting the concrete, expelling unwanted air and preventing other forms of cracking.
Frequent applications of an evaporation retarder such as aliphatic alcohol during placement and during the finishing process will help prevent water evaporating from the surface. Prompt application of curing compound is also very important.
Plan adequate joints and cut joints as soon as possible.
Provide shade and windbreaks to protect the concrete from extremes in weather, particularly after finishing. Damp hessian is great for protecting fresh concrete from the sun. Builder’s film and wooden stakes make for an economical wind-break.