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Things to consider when pouring concrete during the rainy season

Pouring concrete during rainy season

Construction projects are planned and executed all-year-round. This means that contractors need to build in some extreme weather conditions, from searing hot and dry temperatures to windy and rainy weather. These factors can all affect concrete and how it cures, but the rainy season can be particularly hard because it brings water and wind.

Contractors need to keep an eye on their concrete structures during the rainy season. Rain can affect the surface appearance of concrete as well as the internal strength. When the concrete is between its initial setting time and final setting time, the rain can leave patch marks and pores in the wet concrete. This can disturb the upper layer of the concrete before it can cure properly.

Rain can also affect the internal strength of concrete. If there is consistent and heavy rain for multiple days, the excess water on the concrete can slow down the curing process. This can affect the internal bonds between the concrete particles and make the mixture weaker than intended. Here are some other points to consider when pouring concrete in the rainy season.

1. Extra water in the concrete mixture during the rainy season

If you store your aggregates outside, the rain will make the sand and crushed stone wet. This will add extra water to the concrete mix, so remember to use less water when making a batch of concrete. You will also need to keep an eye on your cement and ensure that no moisture gets into the bags while they are being stored. The cement needs to be stored in a dry environment at all times.

2. Use waterproofing admixtures in your concrete

During the rainy season, consider using hydrophilic crystalline admixtures in your concrete batch. These admixtures react with water and cement to form calcium silicate crystals. The crystals block pores and microcracks in the concrete and prevent water from seeping into the structure. Essentially, they seal the concrete and protect it from excess water damage.

3. Avoid pouring concrete during heavy rains

Make sure that the weather conditions are not too wet or windy before you decide to pour concrete. Keep an eye on the weather forecasts and try to find a gap of at least 12 hours where there is no rain. Fresh concrete needs about 12 hours to start the curing process and any rain could affect this. The wind can also have a negative impact on the curing process. Strong winds can cause bleeding in the concrete and affect the evaporation rate of its internal moisture.

4. Rain can cause delays

It is a well-known fact that rain can affect traffic. This can create delays for the transport and delivery of concrete batches. Suppliers need to keep an eye on the weather and avoid making deliveries during the rain. If this is not possible, then drivers should plan to use alternative routes with less traffic. Any delays in delivery will be costly to the project and will allow excess water to affect the construction site.

5. Use waterproof covers to protect concrete

Plastic sheeting and waterproof canvas should be kept on-site during the rainy season. Once a concrete batch is poured, cover it with the sheeting to shield the concrete from the rain. This will keep moisture in the concrete and keep excess water out. Waterproof covers can also be used to protect aggregates and keep them dry.

6. Perform inspections after the rain

Once the rain has subsided, asses the concrete and see if there is any damage or pools of water on the surface. A simple scratch test can be done to see if the surface of the concrete has been affected by the rain. If there is any surface damage or dimples left by the rain, contractors can use a float to remove excess pools of water and smooth the surface of the concrete at the same time.

The key to ensure the success of a building project during the rainy season is preparation. Be ready for heavy rains and have the right equipment and materials on-hand to deal with the wind and water. Pouring concrete in the rain is not advisable – rather stop and wait for the rain to pass, then remove the surface water in the foundations or on the already-poured concrete before completing the pour.


LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 


LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.


At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.


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