What is Concrete Leaching?

If you’ve ever noticed those white stains that occasionally appear on concrete surfaces, you’ve seen the results of concrete leaching. This is a fairly common problem with concrete in Australia, particularly surfaces that are regularly exposed to moisture. You may have noticed these stains on walkways, in car parks, or somewhere else.

While concrete is an incredibly dynamic building material, it does experience issues from time to time. Below, we’ll take a closer look at what causes concrete leaching.

Concrete leaching is a common issue that causes stains to appear on your concrete surfaces. The stains are the result of water seeping into the concrete through small cracks and causing a chemical reaction with the particles within the concrete.

Once enough moisture has entered your concrete, it dissolves the calcium hydroxide within the concrete makeup. Then, once the calcium hydroxide comes into contact with the air, it reacts with carbon dioxide, creating calcium carbonate. This calcium carbonate is carried to the surface when the moisture within the cracks evaporates or is forced to the surface by pressure, usually around cracks or fissures.

This process is how concrete leaching stains come about.

These stains inevitably become an eyesore in your space, particularly if they are exposed to passers-by. Often, the stains also consist of dirt and grime, which may have sat in the cracks for some time. This exacerbates the problem, creating darker and more visible stains.

Concrete leaching is also known as efflorescence, and can also occur on brick surfaces, and even concrete that has a surface coating, where the coating might be compromised.

Concrete leaching will continue to occur if the source of the problem is not addressed. That means that if water or moisture continues to seep into your concrete floor, walls, or even your ceiling, leaching may still occur. However, in some cases, over a long period of time, concrete leaching can cease on its own.

Leaching may self-heal completely if the water becomes supersaturated with minerals, creating deposits of calcium carbonate in the cracks and fissures. This then blocks up these holes and stops moisture from entering later on. As a result, the leaching no longer occurs.

Once concrete leaching has begun to occur, it can be difficult to deal with. The key here is to ensure that further water or moisture cannot enter the concrete. Therefore, it’s essential to seal up any cracks and fissures that may permit water to enter the slab, walls, or ceilings.

The stains themselves can usually be removed by thoroughly cleaning and scrubbing with clean water. The longer the stains are left, the more difficult they are to remove. Therefore, it’s important to tackle the problem quickly. If scrubbing with water does not work, a mixture of vinegar and water or citric acid and water may do the trick.

Preventative measures are essential, and there are a number of ways to reduce the chance of concrete leaching on or in your building. Primarily, much of it comes down to the type of concrete that you choose to use in your building and the components within the concrete mix.

To reduce the chances of concrete leaching, you should choose concrete that:

• Is of high quality and does not contain too much water.
• Is made from cement that is low-alkali, so that sodium salt doesn’t seep out later and create stains.
• Contains sand and gravel that have been pre-washed, to remove any minerals that may cause leaching down the track.
• Utilises a moisture barrier beneath the slab, so that moisture doesn’t seep up from the groundwater in your soil and through the slab, as this can then appear as leaching.

Concrete leaching should be addressed, and can’t simply be left to its own devices. This is because, over the long term, leaching can affect the structural integrity of your masonry. It may become dangerous if leaching is not treated in a timely manner.

On top of this, untreated leaching can cause corrosion to the reinforcing mesh within your concrete, which also greatly impacts the strength of your concrete. Therefore, it is important to treat your concrete leaching problem quickly.

Leaving concrete leaching for long periods of time will only make things worse. Therefore, swift attention should be given to any stains that pop up on your concrete surfaces. In the long run, your building will be better off for it!