A Ronimix Concrete Guide to Working with Concrete – Hot Weather & Drying Winds

More than sunscreen is needed when working with concrete!

The sun’s out, temperatures are soaring perhaps to the mid to high 20’s C, yes it does happen even in the UK … remember however, always resist the temptation to don shorts and vest when working with concrete, especially in hot weather.

This is a health warning we take very seriously at Ronimix Concrete, every delivery ticket of ours has a health warning and we train our teams and kit them out with the appropriate gear to ensure they don’t get burnt by the corrosive properties of cement.

Many builders would have had their health and safety training to work with cement, the key constituent of concrete, but it is always worth repeating this warning, especially for the DIY’er. Cement can cause caustic injury, resulting in chemical burns to any part of the body it comes into contact with.

So cover up and wear protective clothing and gloves, a drop of sunscreen on the sweating brow wouldn’t come amiss either!

Ronimix Concrete believes a temperature between 10 and 20 degrees C is ideal for placing concrete: site mixed by our efficient volumetric equipment, giving good working time, a reasonable initial set in around 3 and up to 18 hours (cold weather) with curing between 7 to 14 days depending upon the load bearing capacities that the project requires.

Concrete can set and reach a solid state as quickly as a couple of hours in hot weather or drying winds, always helpful as it allows builders to access it, however such weather can lead to problems of shrinkage and cracking or even failing to meet its desired strength!

Following our TIPS builders can compensate for these conditions and in combination with the Ronimix Concrete efficient volumetric concrete lorries and the suggested protective measures to prevent rapid evaporation, quality concrete can be poured in hot temperatures and or in drying winds.

In the UK sustained very high temperatures are seldom encountered so we haven’t faced the extreme of needing to add ice to our mix. To date we have also not found any requirement to cool our depot stockpiles, but as global warming increases the risks of higher temperatures this is something we could do. Additionally our trucks are regularly replenished thereby minimising temperature increases during the day.

Planning and manpower

Builders generally want to get trenches or slabs concreted as soon as they are ready, approved by building control and or to avoid risks of damage to the formation by bad weather.

Using our site batched ready mixed fresh concrete results in builders avoiding the issues of drum mixed concrete where over mixing of the concrete after water is added can increase the temperature of the concrete resulting in it setting faster or being faced with large quantities of concrete left in a heap ‘drying out’ before the site team can get it placed.

Ronimix Concrete’s experience allows us to time schedule deliveries 6 days a week. Often we can accommodate same day deliveries, particularly on Mondays and early in the week … we can of course guarantee next day deliveries.

Our time scheduling allows our customers to plan and have sufficient manpower to reduce the total time between the start of transporting, placing and finishing processes and the application of curing procedures to the concrete.

On larger projects, Ronimix Concrete can double up their volumetric lorries to ensure an uninterrupted delivery flow of fresh quality ready mixed concrete. Utilising Ronimix Concrete’s fleet of volumetric on site batching lorries and ground in line concrete pump trucks most continuous pour jobs can be accommodated.

Ronimix Concrete’s own coordinated concrete pump hire service can also speed up transporting the concrete, reaching hard to access areas delivering it straight to where it’s being poured, saving time, manpower and reducing the adverse effects of hot weather.

Damping down

Builders are normally faced with getting rid of unwanted water on site, especially in the bottoms of trenches but in hot and drying wind weather conditions a light spray of cold water over the construction area, trench side, shuttering and reinforcement can greatly assist in reducing rapid evaporation. Doing this the evening before can be particularly beneficial.

Reducing the effect of the sun

On smaller projects protecting the concrete from the sun and from it drying out the concrete too fast should be achievable: particularly consider laying slabs after the walls and roof are in place or erecting temporary sun screens or windbreaks to reduce stiffening or crusting. This helps to minimise rapid water evaporation in the concrete which in turn helps in reducing / eliminating the cracking or crazing of the finished product.

Construction joints

In very hot weather it is worth considering an increase in the number of control expansion joints. Always consult your designer or structural engineer for specialist guidance to plan and properly space these control expansion joints.

Controlling evaporation

Rapid water evaporation from concrete can have a negative effect on the surface layer of the concrete. This lack of water can lead to weaker concrete especially at the surface of the slab or foundation. This means the concrete will be more susceptible to cracking and or even failing. When rapid evaporation occurs, the finished and cured concrete will have a sandy, powdery finish.

To control rapid evaporation … hand float the concrete promptly after the water sheen disappears, or when the concrete can support a finisher tool. Also, after which consider using a proprietary Evaporation Retarder to seal the concrete surface; and or cover the entire area with heat reflecting polythene sheeting or damped down sacking, hessian or waterproof paper and removing same later the next day following the initial set.

Treatment for Floor Screeds

Ronimix Concrete site mixes floor screed using sand, cement and water, discharging the required quantity on to polythene sheeting for the builder / screeder to place. It has a limited workability of up to around 2 hours depending on temperature so protection and an adequate, efficient workforce is required. However, if specified a retarder can be added, offering circa 4 more hours of working time.

Curing the concrete

Moist water curing is most needed during the first few hours after placing and finishing the concrete. In hot weather, continuous moist curing for the entire period is preferred. Treatment as above noted will aid this.

Where Formwork is used, this should be loosened as soon as possible without damage to the concrete. Then, water should be lightly sprayed on exposed surfaces and allowed to run down inside the shuttering.

Similar to the above, if moist curing can’t be continued beyond 24 hours, protect the surface from drying with curing paper, heat reflecting plastic sheets, or membrane forming curing compounds while the surface is still damp … see also Controlling evaporation above.

Summing up

Builders working in the UK are unlikely to experience the temperature extremes regularly faced elsewhere in the world where quality concrete is required. Although rare, Ronimix Concrete offers these preventative TIPS to remind builders and DIYer’s to be aware of such weather conditions particularly since concrete or screed failure can be expensive to rectify and “its always better to be safe than sorry” so to speak!