The Severity of Rust Stains

18 October 2019
By Chris

Rust is a common sight in structures where its structural strength comes from iron, steel, and other kinds of metals. Depending on the metal, these yellowish-brown or sometimes reddish patches emerge as a result of oxidation, which is usually caused by the presence of moisture and dampness. The minerals in the water react with the metal setting off the reaction which causes the rust. But it is because we see rust everywhere (bike chains, screws, etc) that when we see it on a building, we think little of it when in truth rust is often an indication that things under the surface are far from rosy.

The presence of rust is a manifestation of corrosion, a potentially serious issue which can lead to structural issues. Because rust is a swelling on the metal, it pushes the surrounding materials outwards, causing more moisture to get in which thereby weakens the strength of the structural material. Thus, much like the iceberg that sank the titanic, if you only look at the parts you see, you will miss the devastation that awaits under the surface.

So the purpose of this post is to help you realise the reasons why rust stains exist and why they pose a serious danger to your building.

So how is rust formed?

Whenever steel and other metals containing iron are regularly exposed to oxygen and moisture, they form rust. Simply put, whenever there are air and the presence of water, many metals will oxidise, a process called corrosion.

But why does rust form even if steel reinforcement is buried deep within the structural foundation?

There are actually many reasons why concrete cancer, or the process by which structural steel within a concrete slab begins to rust, occurs.

It can be because of poor and rushed construction of a building. With bad workmanship, the rebars may not be properly covered or correctly distanced from the surrounding materials, thereby speeding up corrosion whenever moisture is present.

Another cause of concrete cancer is inadequate waterproofing. If waterproofing was neglected during the construction stage, whether due to budget limitation or substandard waterproofing works, you can expect water to seep through the substrate easily and for concrete cancer to eventually affect your structure. All it takes is a hairline crack to occur as part of the settling phase, and it is enough for water to get in and go to work.

Why is rust dangerous?

Rust may seem trivial but did you know that it is one of the most serious causes of structural failure?  In fact, over the centuries, it has led to bridges and buildings needing to be torn down. It has also triggered a mid-flight crisis due to a weakened fuselage and resulted in the uselessness of some ships, airplanes, and jet planes as well. Rust is everywhere and it is an expensive problem. A 2002 study by NACE (the eminent body for corrosion around the world) found that in America alone that rust causes damage per year of $276Billion.

Yes, rust may look harmless, but the tell-tale orange flakes are an indication that weakening of the metal has already begun.

If not treated sooner than later, a metal which is encased in concrete and is rusting will lead to concrete cancer and spalling which will not only weaken the structural integrity of a building but also impact the quality of life of the people living or working inside the damaged structure. Plus, safety and health could be compromised through falling concrete, which would lead to costly reparation and associated expenses.

When to take rust stains seriously

Damage Column At Cherry Brook Shopping Centre - Concrete Repair - Remedial Building Services


If you believe that rust is a simple issue, here’s some bad news for you. Rust stains are actually a manifestation of how bad corrosion has become. When you see them staining your concrete and pushing it out, it actually means that the damage has become problematic enough has started spreading from within the concrete to the concrete surface! Simply covering it up with paint or a patch of concrete will never solve the problem. It may mask the ugly sight and fix the aesthetic aspect but in reality, it is just a Band-Aid solution.

Similarly, if you think scratching the rust off from the surface will eradicate it, you’re mistaken again. Scraping rust off from walls or concrete only removes the tip of the iceberg, it does not stop what is underneath from continuing.

Prevention is better than a cure

If you are a builder, looking to prevent the chance you will be called back within the Home Warranty Period, then ensure that during the construction phase, that you take adequate steps to prepare the surface and treat the steel. Abrasive blast cleaning compliant with ISO 8501-1 prior to the application of a protective coating should be followed. Then take steps to waterproof those areas which are prone to volumes of water to ensure they remain impervious to leaks.  A drainage break should be considered as well in order to avoid the retention of water and dirt at the junction plates.

As mentioned earlier, proper waterproofing also plays a big role in the prevention of rust, and ultimately, concrete cancer. There are many systems that you can choose from: from torch-on membranes to liquid waterproofing, you can ensure that water will never seep through the concrete and reach the rebars used for the foundation. If you need more information, read about the different types of commercial waterproofing that you can take advantage of.

While prevention is always better, there are instances when concrete cancer appears despite precautionary measures. In this case, you will need to find a rust solution that will guide you on how to remove rust from metal effectively. Nevertheless, it is still best to get in touch with structural management experts in order to find the most appropriate treatment that will not aggravate the damage caused by rust.

How Remedial can help you address rust stains and concrete cancer

If you see rust “leaking” from inside the walls, the biggest piece of advice everyone at Remedial Building Services will give you this – treat it as early as possible.

When it comes to repairing concrete cancer and structural waterproofing, see to it that you are consulting an expert company like Remedial. We will work with you to identify the source of the moisture, repair that and then undertake works to ensure the rust is eradicated from the structure itself.

With us, you are provided with long-term solutions that will preserve the strength of your structure. Why would you go anywhere else, get in touch with us right away!