Ruukki Cor-Ten®

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Zuzanna Jastrzebska
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Ruukki CorTen panel is a type of cladding product made almost purely from steel. Thanks to the natural patina layer that forms on its surface when exposed to rain and sun, it works like a protective external envelope of a building. With its characteristic rusty raw material aesthetic, it has become very trendy in architecture in recent years. Architects have been eager to choose it over other cladding steel of this type because it does not need any synthetic protective layers to prevent corrosion, so it seems more sustainable. However, the reality is that CorTen is just replacing toxic varnishes with a similar volume of steel layer, one of the most energy intensive and pollutant materials to manufacture. As a result, it turns out to be exceptionally demanding. If not inspected regularly, it may cause serious damage to the building. Although CorTen is limited to a certain type of application, the Ruukki does not provide any design support service that would enable builders to make the right choice for their project, which in consequence can lead to some unsustainable uses of the product. Although Ruukki has introduced a promising sustainability plan, some of its points are too vague and undeveloped, which makes it’s effectiveness quite questionable.

What it's made of:


CorTen is very much appreciated in architecture. These thin steel panels with characteristic natural rusty colour have been appearing on buildings more and more in the recent years. Apart from the appealing design, architects praise the product for its corrosion resistance, which is believed to be better than other types of cladding steel. Although, is this really the case? Yes, the protective patina layer, which is oxygen impermeable, effectively prevents the deeper parts of the metal from oxidizing. The layer forms itself through the passivation process, which is the reaction of the metal with oxygen in the moisture environment, resulting in a natural metal’s protective layer, preventing deeper metal oxidation. This eliminates the need to use all toxic paints, varnishes and other highly processed products that are not compostable and heavily pollute the environment during their life cycle. 
However, in practice it is not as simple as it seems. To achieve this effect, strict conditions must be provided. Otherwise, the metal will uncontrollably patinate, which then can weaken some structural elements. The steel has to be wetted and dried repeatedly without any excess amounts of water, resting for a longer period of time on the surface. Plus, it can’t be directly touching the wall on which it hangs, to save other parts of the building from an expanded corrosion process. To add to this, the rust sometimes washes out, leaving stains on the surrounding pavement. This results in extra costs and maintenance to repair the damage. 

In regard to the environment, the advantage of this product is that it can be produced from pre and post consumer recycled steel, reducing the demand for raw material. The company, however, does not reveal how much of the production is really from the recycling resources. Although, they do mention that the steel can be recycled at the end of its lifecycle without explaining how? Personally, I find it a bit hard to understand how half oxidised metal can be alloyed into another quality product. In short, its environmental aspects seem promising, however without a logical explanation and more transparency, it cannot even be evaluated.

How it's made:


Ruukki as a company that specializes in steel manufacturing, and CorTen is one of their flagship products. Steel in general has an extremely bad reputation in the area of sustainability. Not only is it responsible for up to 9 % of global emissions, but its production technique is known to be one of the most hazardous manufacturing processes out there. According to the company’s operational strategy, it seems like they’re trying to eliminate the negative impacts of their factories. The most important stage of CorTen’s production, and simultaneously the most problematic, is mixing boiling hot steel with copper and chromium. Although this process is very energy intensive, Ruukki has been increasing the use of wind energy in their factories. Their goal is to produce fully fossil-free steel by 2026. While this sounds optimistic, it looks like the Ruukki has omitted the problem of unsustainable excavations, not even mentioned on their website. Overall, mining of iron pollutes water with heavy metals and acid, so the bad effects are very serious. Unfortunately, without transparency on this topic, it’s imponsible to even evaluate Ruukki’s actions. Moving back to positive sides, the company claims that it makes a great use of the steel’s recycling property, planning to increase the use of recycled material in the production. Still, this aspect also needs more transparency to ensure the liability. 

Who makes it:


Ruukki is a supplier of steel-based building products and services for roofs and walls, operating under the Swedish company SSAB, present in 10 European countries. They share the same values and follow a common sustainability programme that sets a goal of fully fossil-free steel by 2026. The company’s approach is to increase the use of reneweable energy systems and replace the coal with hydrogen gas in some of the important production stages. The details of this strategy are possible to find only on the general SSAB website. Ruukki would definitely benefit from presenting this info on their own site as well, making it clear for the customer what these sustaianbility strategies mean in practice. 
Apart from the paternal firm goals, Ruukki has created their own unique action plan based on three principles: responsible partnering, sustainable offering, and operations. As for the last principle, the leading goal is to reduce emissions by 25% with a deadline by 2026. How does this relate to the total amount of their own and global emissions? Will this make any positive difference in the fight with climate change? This is not explored deeper in the information that the company shares. This is especially important for steel manufacturers, as they are considered one of the biggest GHG contributors globally. Moving onto the second principle - sustainable offering, this means that the company’s goal and value is to be able to provide the customer with mostly environmentally friendly products. They are aware of how big of an influence they have on other industries and sectors so any change towards sustainability will have a continuous positive effect. Closing this section with the principle of responsible partnering, this seems to be the weakest part of the plan. Citing from the website: “Ruukki aims to become the safest company in the construction product industry,” and that’s it. What does this mean? Does it mean no injury work politics, or rather having a great ESG score, making the investment “the safest” bet for stakeholders? To sum up, even though the company’s intentions seems great, the plan is too vague and undeveloped to even evaluate the potential effectiveness of it.