Your contractor is ready to start work on your new project, just as the cold weather hits South Africa. Will cold weather hurt your cement-based finish? We explain what the effect of cold and freezing weather is on cement-based finishes and why precaution needs to be taken when working with cement in very cold conditions.
Most liquids have a quite simple behaviour when they are cooled - in that they shrink in volume. Water is one of the few exceptions to this behaviour. When liquid water is cooled, it contracts like one would expect until a temperature of approximately 4 degrees Celsius is reached. After that, it expands slightly until it reaches the freezing point, and then when it freezes, it expands by approximately 9%.
It is very important to be aware of this property of water as the expansion of water from 4 degrees Celsius downwards can permanently damage fresh cement finishes. Even the smallest expansion of water will break the fragile cement bonds which have a very low tensile strength in the early stages of hydration and these bonds will never reform.
Most damage occurs in cement-based coatings, thin slabs and exposed corners as these cool rapidly in winter conditions. Bigger castings are protected by the heat given off by the hydration process. The effect is intensified on cold days as the cement hydration process slows down at low temperatures, which delays the development of tensile strength. Cement products should not be applied if temperatures below 5 degrees Celsius are anticipated – indoor winter temperatures in South Africa seldom get as low as 5 degrees Celsius, however inland night temperatures in winter often fall below 5 degrees Celsius.