A GUIDE TO POURING CONCRETE IN THE RAIN

Information · 9th August 2018

A sudden downpour of rain is enough to make even the most experienced building contractor rethink a concrete pour. As ready mix concrete suppliers in London, we’re all too familiar with unpredictable weather, but there are ways to successfully protect your project from excess water. Read on to find out how to protect concrete from rain.

HOW DOES RAIN AFFECT CONCRETE?

Rain falling on top of freshly laid concrete can damage the surface and compromise a level and floated finish. Even worse, if too much extra water works its way into the concrete mix, this can result in weak concrete overall.

For this reason, it’s important to never lay the concrete onto wet surfaces or trenches filled with water if there’s a risk that the water may mix into the concrete. It is often possible for the concrete to displace the water, pushing it upwards and out of the cavity. Don’t try to ‘soak up’ the water with the concrete, or work it into a freshly laid surface as this excess water will compromise the concrete mix.

How rainwater will affect concrete depends on the stage in the curing process that was reached before the rain set in. If the concrete is still fresh (around 2-4 hours after pouring), it’s important to cover the surface to protect it. However, once the concrete has been finished (between 4-8 hours after pouring), and has set enough for walking on, the effects of rain should be minimal.

HOW CAN I PROTECT CONCRETE WHEN IT RAINS?

If bad weather is forecast or you’re pouring concrete in the rain, your first step should be to protect the work site with a plastic sheet covering. Before you start the pour, make sure that any cavities are free from water, and keep them covered as much as possible. If it started raining before you could cover the slab, don’t panic. Simply wait until the rain has passed, then push or pull the water off the edge of the surface before finishing. This is sometimes done by sliding a garden hose across the surface of the slab, wiping away the water.

HOW CAN I TELL IF RAIN HAS DAMAGED THE CONCRETE?

Once the rain stops, it’s time to assess any potential damage to the concrete. Obvious defects should be easy to see during a visual survey, while the abrasion resistance can be tested with a scratch test – simply use a screwdriver and compare the result to other areas known to be of good quality. At this point, surface damage may be easy to repair using some extra concrete. However, if areas of a thin slab are compromised, it may be better to remove the damaged concrete and replace full depth sections. If you require any additional concrete to make repairs, contact us to arrange your order, with same or next day deliveries available in Watford, Harrow and the surrounding North West London areas.

TOP TIPS FOR POURING CONCRETE IN THE RAIN

-Plan ahead: Check the weather forecast on the day of your pour.
-If rain is forecast, make sure you have plastic sheeting or waterproof materials available to cover the work site.
-Check that the surfaces you are pouring onto are dry before you begin. Never pour concrete into water-filled cavities or wet surfaces from which the water cannot be displaced and escape.
-After the storm, conduct an assessment of any damage and carry out repairs (if necessary).Always consult with your main building contractor or call the friendly Master Mix Concrete team for further advice.

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