Builders Merchants Journal – BMJ Publishing to Builders Merchants and the UK merchanting industry for more than 95 years
What can extreme temperatures mean for masonry construction – and what advice can merchants pass onto customers working with bricks and concrete over the summer months?
The weather is always the go-to talking point for us Brits – the recent heatwave and blanket media coverage reinforced for us just how fascinating a topic it can be. And for those in the construction sector, or indeed any keen DIYer tackling projects over the summer months, the extremities of the great British weather can throw up some real challenges. So, what do merchants need to know to help their customers prepare for working in the heat?
Curing
Let’s look at how hot weather can affect concrete and mortar where it’s critical to get conditions right.
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.
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 from occurring is to ensure that the mix is in a moist condition after it has set. Simple solutions for your customers 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).
Remind them, 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.
Protecting bricks
It’s not only the mortar that needs consideration. In extreme heat, bricks are drier and will suck more water than usual out of the freshly placed mortar. Too much suction will result in poorly hydrated, low strength mortar. Storing bricks in the shade will prevent this and dampening the bricks before use will also help to control the suction.
Your customers will need to think about the working conditions. Simple measures can help – again, using cool, mains water or, if this is not possible, keeping any stored water cool. And, although it may sound obvious, consider scheduling work to avoid hot afternoon periods.
Colder weather
It’s also worth thinking ahead to the winter months – cold weather can have just as much effect on the usability and strength of concrete. For instance, 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 if your customers avoid 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, they should 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 and leaving opened cement outside will, naturally, 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. For customers working in windy conditions, they should consider putting up wind barriers to protect their work and cover the work with plastic sheeting.
Rain can, too, cause problems for your customers They can avoid working rainwater into the mix as it cures by covering your work with tarpaulin or a waterproof sheet. This will both help with curing and will prevent rain marks on the finished surface
Planning ahead
Careful planning and preparation is important to ensure successful masonry work this summer. It could be the key to a seamless summer of construction for your customers – and offering some good advice on the way will do your reputation no harm either!
Garry Gregory is packed products manager at Tarmac
