Its that time of year again when we get asked if its OK to concrete or lay bricks during during the cold and snowy weather. As general advice we would not recommend working when temperatures are below 5 degrees and falling unless additional precautions are taken.

Cemex have issued some excellent guidance about the need to protect concrete in cold weather. If young concrete is allowed to cool much below freezing point it will be damaged to such an extent that it will be unfit for use. It should also be noted that even if temperatures do not drop below zero the concrete will develop strength much more slowly than during the warmer months.

The key temperature for concrete is 5 degrees and the guidance can be found at http://www.cemexliterature.co.uk/pdf/Concrete_ColdWeatherConcrete.pdf

Cemex have also produced guidance on bricklaying during bad weather. Setting in mortar usually occurs at temperatures above 4 degrees C. If mortar is used below this temperature it may not set properly and if water is retained in the joint, frost damage can result. 

Fortunately there are relatively few periods in the UK when the daytime air temperature remains below 4 degrees C and if it is below freezing it may be impractical to continue with masonry work in any case; not least because the outdoor water supply will freeze.

However, during the winter months all stocks of bricks and blocks should be covered to provide protection against rain, frost and snow. Bricks or blocks that become saturated should not be used until they have dried out and in cold weather they risk damage if they freeze.

Mortar likewise needs protection during very cold weather. If mortar freezes during storage any frozen material must be discarded. Neither should mortar be laid on frozen surfaces. Anti freeze agents for mortar are not recognised in British or European Standards.

As mortar hardens and develops strength more slowly in cold weather, new masonry, or areas under construction, should be covered and protected from the elements. This is likely to require two layers - thermal protection such as hessian or some form of quilting and a waterproof sheet to stop the under layer getting wet.

Protective covers should not be in contact with the face of the wall to avoid ‘sweating’ and consequent staining. The covers should be secure and kept in place until the mortar dries.