Can You Pour Concrete In The Rain?

When making your own home improvements, sometimes answers to questions like this one might seem obvious to seasoned professionals. But knowing the answers to these types of questions can be the difference between a professional-looking finished product and a shoddy-looking DIY job. 

It’s true that water is a key ingredient in all concrete, giving it the ideal consistency it needs to pour evenly over a surface and enable you to smooth it over easily before it dries. But, adding water, like in the form of pouring rain, to already mixed concrete can affect its consistency and lead to problems in its strength after it has dried. 

It’s important to avoid starting a cement pour if you know it will be raining in the next 48 hours or so. However, if rain has already gotten onto the surface of the cement, we provide some tips on what to do, as well as how to plan ahead in future and what to do to prevent damage from rain on wet concrete. 

Is rain good for concrete?

The short, simple answer to this is “no”. However, a light drizzle shouldn’t affect it that much, it’s more when there is a deluge that you should worry. We advise that before starting to pour concrete, you check an up-to-date weather app or website, especially in the rainy months in Perth. If rain is expected, it’s best to postpone a big concrete pour until after the rain has stopped. 

Despite the feats of modern technology, sometimes an unexpected rain shower can catch you unaware. In this case, you should use a concrete covering such as a piece of plastic or a tarp and place bricks or heavy rocks on the edges so that it doesn’t blow away and rain can’t seep underneath. It’s also important to scope out the area where the concrete will be laid beforehand and look out for any gutters or natural troughs in the ground that would direct water to the allocated area and try to redirect the water flow away from the area as far as possible. 

How to prevent damage from rain on wet concrete

If heavy rain is predicted a day or two before the pour, cover the area with heavy plastic to prevent it from becoming saturated. If it rains on the area that is reserved for a cement pour, the subgrade can become oversaturated, causing water to seep through and change the water-cement ratio.

Pouring concrete is not as easy as it seems and there are a lot of things to consider. If you lack confidence and are unsure of whether you are doing it correctly, it is best to use the services of concrete professionals. A professional concrete company will avoid scheduling concrete installations on rainy days and if an unexpected shower does occur, they will do their best to minimise the risk of the concrete being compromised.   

Once the damage is done, it can be hard to rectify the situation. It’s not just a case of adding more concrete powder to the mix to try and restore its form as this could lead the finished product to appear ‘gravelly’ and uneven. If water does get onto the top of the concrete, once the rain has stopped, make sure to brush the water off of it. 

How long does concrete take to dry?

Cement generally takes about 4 to 8 hours to dry after a pour. If you managed to finish pouring the cement before the rain started and it was given enough time to dry and set, even if not completely, water on the surface can actually be beneficial as it can hydrate the concrete and help in the curing process. 

If rainwater does get onto the top of your poured concrete and you’re worried it may have been compromised, you can do a simple scratch test using a screwdriver or the Mohs concrete surface hardness scratch test kit to check if the rain water had any impact. 

What to do for rain-damaged concrete

If an unexpected downpour lands on your not-yet-dry cement, it’ll probably wash some of the cement out of the concrete, which might cause other problems when it eventually does dry, such as surface scaling and surface cracking. If the concrete is coloured, rain may also wash away some of the colour and cause streaking. 

If it’s only the surface layer that has been damaged, instead of removing the whole block of concrete and starting over, the best solution would be to grind the concrete down to where the damage begins and resurface it. 

It’s also important to apply a sealer after the concrete has dried as this will prevent it from starting to bubble and blister. Make sure that there is no rain forecasted for the next 24 hours before applying the sealer.