Why does my concrete have white spots?

Have you noticed unsightly white spots appearing on your concrete? Are you wondering what they are, why they’re there, and how to get rid of them? 

In this article, we’ll shed some light on these strange white patches so that you can give your concrete the best chance of staying free from blemishes. 

Why do white spots appear on concrete? 

The official name for white spots on concrete and other materials is efflorescence, which is essentially salt residue. 

Efflorescence is caused by water-soluble salts within the concrete material coming into contact with excess moisture. This moisture is either a result of excess water being added at the point of mixing or from an external source of moisture such as a nearby leak.

As the moisture evaporates, salt will be moved upwards from inside the concrete to the surface through capillary action, leaving behind a white stain on the concrete. 

There are two types of concrete efflorescence: 

• Primary efflorescence: White stains that appear within 72 hours of laying, usually as a result of excess moisture being put into the mix itself during preparation. 
• Secondary efflorescence: White stains that appear after 72 hours are often caused by external moisture sources. These stains can develop days or even years later. 

So, how can you reduce the likelihood of white spots appearing on concrete? 

How to prevent white spots on concrete

White patches and discolouration on concrete can be a real eyesore and a complete headache. To stand the best chance of avoiding their appearance, you should always use a reputable, accredited concrete company such as Sussex Ready Mix Concrete to ensure that best practices are followed and only the highest quality mixes and products are used, without too much water being added at the mixing stage. 

Please be aware that even after using a highly regarded company, efflorescence can still occur due to external factors, such as rainy weather at the point of laying, a high water table or a leak. These external factors can either be difficult to control or may go undetected until they are an issue. 

How to remove white spots on concrete 

If it’s too late and you already have efflorescence, how do you get rid of it? 

Initially, you should try and identify the source of the problem if it’s external. Check for any nearby leaks or potential water sources that could be contributing to excess moisture, and rectify this first or the problem will appear again. You may not always be able to pinpoint the cause but it’s always worth investigating first. 

Pale efflorescence may go away on its own in due course but if you want it gone now, these are the three main methods to try: 

• Sandblasting is a common method used to remove white stains but it can sometimes damage concrete or harm its appearance so make sure to do it lightly.  
• You can attempt to wash off the white spots by gently scrubbing the area with clean water or a dry brush. Whilst you are doing this, any standing water should be removed using a fan or wet vacuum to avoid exacerbating the moisture problem. 
• There is the option of using commercial water-based cleaning products to remove the stains or a dilute acid solution, but make sure the concrete is properly sealed before doing so. It is also worth testing your solution or chemical of choice on a small test patch of concrete to ensure it won’t have a detrimental effect. 

If the efflorescence is severe, or is accompanied by other issues in the concrete such as damage, cracks or structural problems, it may need relaying, something that our team can help you with. 

Here at Sussex Ready Mix Concrete, we’re the number one supplier of high-quality concrete mixes for Sussex. As a family-run company with an outstanding reputation, we’ll only charge you for the concrete you actually use and will work to best practices to ensure a great result. Get in touch to discover more.