Building Envelope blog posts
Ruukki Cor-Ten steel in a student assignment
Elli Hirvonen, Architectural student, Aalto University | May. 5, 2020
During the spring, the second year students of the Aalto University Department of Architecture attended a course in architecture and engineering, accepting an assignment to design a living and working space for an artist. Although the house would never be built in reality, a group of Helsinki-based artists were chosen to play the client’s role. Conceptual design started by interviewing the client and their wishes.
My own imaginary house was located on the Pietarinkuja street in the Eira district of Helsinki. The long, narrow plot provided plenty of inspiration, and I wanted to design a building that would largely integrate with the environment and provide functional spaces for both living and working.
In addition to the architectural entity, the assignment requires attention to building materials and related structural solutions. Weatherproof Cor-Ten steel was a natural choice to use as the building material, enabling a sculptural and monolithic facade. Steel is easy to mold and bend, which enabled hiding the gutter on the slanting roof, for example, and excluding the eaves from the drawings. Since the lot is located near the seashore, I wanted to consider the sea winds that are hard on the facade in my design. I also felt that the rusty-red tone suits the colourful, plastered facades of the surrounding buildings.
It was exciting to learn to know a building material new to me and how it behaves in a facade. My background study included scanning the various types and sizes Cor-Ten panels and the surfaces feasible to use in a facade. Flexible steel material allowed many alternative sheet layouts; the overall look is highly dependent on whether the sheets are laid out evenly or unevenly, whether they are perforated or not and so on.
Another task was to build a 1:10 scale model of the facade. The objective was to experience the materials of the building and present its facade surface as realistically as possible. At first I considered
presenting the steel with cardboard painted in rust color, but I decided that it would look too crude to imitate steel surface. As I didn’t know where to obtain Cor-Ten steel on a short notice for the scale model, I contacted Ruukki directly and asked if I could purchase just one square metre of the material. To my surprise they soon replied that Ruukki would be happy to cooperate on a student project and wants to donate the material that I needed. My square sheet of steel arrived in a couple of days, and I managed to pick it up a few days before my assignment was due.
As I was finalising the scale model, I ran into something that taught me a lesson: the Cor-Ten colouring features. For some reason I had thought that the surface would be rusty already when delivered from the factory but this was not the case. The steel was stainless. I nearly panicked trying to figure out how to make the surface rusty on time before my submittal. The problem was solved quickly as the Ruukki office called me on Friday afternoon and gave me clear instructions on how to make the sheet rust quickly. I needed to wipe the protective oil off the surface with paper and then spray the sheet with slightly salty water. I did as instructed, and the surface turned rusty in just a few hours! As I was gluing the scale model parts together at the workshop, the piece of steel had time to develop rust on its surface. After spraying it again a couple of times I achieved a beautiful rust-red tone. Then all I had to do was to cut the sheet with metal cutters into correctly sized pieces and attach the pieces into to model.
At the critique session, my scale model received plenty of positive feedback regarding acquiring genuine material and presenting the design intent in a very illustrative way. I am myself very happy with the result and agile cooperation with Ruukki during the project! I was graded full points 5/5 for my work. :)Elli Hirvonen
Architectural student, Aalto University
Read more about Cor-Ten