Dr Bill Price, National Commercial Technical Manager at Tarmac Cement, looks at how the unpredictable British weather can affect working with concrete and offers some useful tips for builders on managing their projects around the elements.
The weather. It’s the go-to topic of conversation for us Brits – and, given what we’ve seen so far in 2018, it’s no wonder it’s an endless source of fascination.
For those working in construction, this rapidly changing weather can throw up real problems – not least for anyone working with concrete where the success of the curing process ultimately depends on the right conditions. During curing, the cement present in concrete and mortar undergoes a chemical reaction with water. This reaction is essential for normal strength development of the mortar. And three factors – humidity, wind speed and temperature – can really make or break this process.
Whilst the unprecedented temperatures witnessed this summer may be cooling down, it’s still important to understand the challenges that hot weather can throw up. At the very least you can be prepared for the next time the temperature rises!
To begin with, higher temperatures will naturally increase the likelihood of too much water evaporating during the curing process. If a mix dries too quickly then it will not only shrink and crack but will also result in weak, dusty and porous concrete. Critically, too, it will also mean a marked reduction of strength.
One simple measure to prevent this is to ensure that the mix in a moist condition after it has set. Common curing methods in hot weather can include covering work with damp hessian or plastic sheeting to prevent evaporation, pre-wetting of surrounding porous materials or, for horizontal surfaces, misting with light water spray at regular intervals (for use especially with mortars and renders).
Remember, too, to use cool mains water where possible instead of storing water in containers ready for use. If it’s not possible to use mains water, it’s vital that stored water is kept cool. Finally, avoiding making up unnecessary large batches of mortar will also help minimise evaporation.
Temperature plays a large role in the usability and strength of concrete. Just think back to the ‘Beast of the East’ and the havoc it caused to UK building projects. This is because if newly placed concrete falls below 0ºC prior to developing enough strength, the water in the mix will freeze and expand which will see cracking, scaling and crumbling of the concrete.
This can be easily managed by avoiding mixing or laying concrete when the air temperature is below 5ºC. It’s also important to keep the mix above 5ºC for 48 hours after the concrete has been placed. If there is any risk of frost during this period, protect with an insulation quilt sandwiched between two sheets of polythene sheeting.
Another significant factor to consider in the colder months is the quality of the concrete mix itself. For example, a product such as Tarmac Blue Circle Quality Assured Mortar is air entrained and, therefore, benefits from greater frost resistance.
Packaging is also important when protecting against the elements. Leaving opened cement outside will affect the product. To help reduce wastage and save costs, Tarmac Blue Circle Cement comes in tear and weather resistant packaging and tubs.
Wind and rain
Severe wind can, just like the heat, cause increased evaporation, drying and cracking. Consider putting up wind barriers to protect your work and cover the work with plastic sheeting making sure, of course, that the sheeting is secure.
Rain can, too, cause problems. Avoid working rainwater into your mix as it cures Again, cover your work with tarpaulin or a waterproof sheet, both to help with curing, and to prevent rain marks on the finished surface
For further information, visit https://tarmac-bluecircle.co.uk