Stone makes wood durable 

If you have visited the Helsinki Olympic Stadium after its multi-year renovation was completed in the fall of 2020, you have certainly noticed the impressive wooden slatted ceiling of the grandstand.  

The roof has over 500 kilometers of battens. The material is Kivipuuta, which comes from the Aureskoski Refined Wood Mill in Parkano. The interior ceiling of the Olympic Stadium grandstand, designed by Arkkitehtitoimisto K2S Oy, received the 2020 Wood Award. 

– Completely fire-safe wood was sought for the Olympic Stadium. Stone wood meets fire requirements so well that a separate automatic extinguishing system, i.e. sprinkler system, did not need to be installed at all, says the CEO Markku Heinonen From the Aureskoski Refinery. 

Stone wood has also been used, for example, in the seats of the Mezapark singing platform in Riga. The 30 movable and stackable Riga benches designed by Piiroinen were also equipped with barcodes to facilitate storage and placement.  

Markku Heinonen thanks the architects for their bold development and experimentation of new solutions. As wood is utilized in public projects, awareness of the fine and ecological properties of wood is spreading more and more widely. 

– Architects are always on the cutting edge of the times. By boldly experimenting with new solutions, they create stepping stones for the direction in which construction is headed, Heinonen says. 

The complex manufacture of an old invention 

Stone wood is not a new invention in itself. Water glass similar to stone wood was patented in Great Britain as early as the mid-1800th century. In Finland, the Aureskoski factory began testing Stone wood in 2015.  

The process is quite demanding. Natural stone, such as domestic glass sand, is turned into a liquid at high temperatures. After this, the silicate obtained from the stone is absorbed into the wood. Once the absorption is successful, the liquid must be returned to a solid form with the help of fruit acids or other natural substances, such as tree resin.  

The silicate fills the cell walls, but the wood remains porous. This makes the material a good insulator and breathable.  

The degree of impregnation varies depending on the intended use of the wood. The strictest possible fire classification requires thorough impregnation, and timber for outdoor terraces is impregnated down to the heartwood. Even the lightest impregnation provides protection against rotting, as the stone wood treatment creates mechanical protection for the cellular wall. 

I use the term mechanical wood protection because the product is made fireproof and weatherproof by crystallizing the aggregate in the walls of the cell. 

The surface will patina to a beautiful grey in about a year if it gets sunlight and gets wet. The surface can also be tinted, as was done on the roof of the Olympic Stadium. Stone wood does not require much maintenance, but it does need to be kept clean. 

– Stone wood has been used for terraces and piers, among other things. The main market is in Finland. The product has also been exported to other parts of Europe and to some extent outside Europe. 

Wood has a future 

In addition to stone wood, Aureskoski produces floorboards, sauna products, interior panels and durable wood. The chips and shavings from planed products are produced as domestic bioenergy in its own pellet factory in Parkano. The chips from planed products are also used to make wood insulation. 

The economic recession has also been reflected in Aureskoski's operations, and the pace of the last couple of years has been slower. Heinonen, who describes himself as a wood believer, firmly believes in the future of wood. 

– We are constantly engaged in product development in many sectors. We are involved in the development of hot water treatment and lignin. By utilizing and improving the natural properties of wood, we can still develop many new things from wood, Heinonen describes.