Stone makes wood durable 

If you have visited the Helsinki Olympic Stadium since its multiyear renovation was completed in autumn 2020, you are guaranteed to have noticed the impressive wooden canopy over the spectator stands.  

The canopy is made up of over 500 kilometres of wooden slats. The material is Kivipuu, “stone wood”, which originates from Aureskosken Jalostetehdas in Parkano. The canopy of the Olympic Stadium spectator stands, designed by architectural firm K2S Oy, was awarded the 2020 Wood Award. 

– “Fully fire-safe wood was needed for the Olympic Stadium. Kivipuu meets the fire requirements so well that there was no need to install a separate automatic fire extinguishing system, that is, sprinklers,” says CEO Markku Heinonen from Aureskosken Jalostetehdas. 

Kivipuu has also been used, for example, in the seating of the Mežaparks bandstand in Riga. The 30,000 movable and stackable Riga benches designed by Piiroinen were also equipped with barcodes to facilitate storage and placement.  

Markku Heinonen praises the architects for boldly developing and experimenting with new solutions. As wood is increasingly utilised in public projects, awareness of the amazing and ecological properties of wood spreads ever further. 

– “Architects are always at the cutting edge. In boldly experimenting with new solutions, they show the direction construction is headed in,” Heinonen says. 

Complex manufacturing of an old invention 

Kivipuu is not a new invention in itself. Water glass similar to Kivipuu was patented in the United Kingdom as early as the mid-19th century. In Finland, the Aureskoski plant began testing Kivipuu in 2015.  

The process is quite demanding. Natural stone, such as Finnish silica sand, is converted into liquid at high temperatures. After this, the silicate obtained from the stone is absorbed into the wood. When the absorption is successful, the liquid must be converted back into a solid form with the help of fruit acids or other natural substances, such as resin.  

The silicate fills the cell walls, but the wood remains porous. Thanks to this, the material is breathable and insulates heat well.  

The degree of impregnation varies depending on the applications of the wood. The strictest possible fire classification requires thorough impregnation, and wood intended for use in outdoor terraces is impregnated down to the heartwood. Even the lightest impregnation provides protection against decay, as the stone wood treatment forms a mechanical protection in the cell wall. 

– “I use the term mechanical wood protection because the product is made to be fire resistant and weather resistant by crystallising mineral material in the cell walls.” 

The surface assumes a beautiful grey patina in about a year if it receives sunlight and gets wet. The surface can also be tinted, as was done on the canopy of the Olympic Stadium. Kivipuu does not require much maintenance, but it must be kept clean. 

– “Kivipuu has been used for terraces and piers, for example. 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 Kivipuu, floorboards, sauna products, interior panels and impregnated wood are manufactured at Aureskoski. The sawdust and shavings of the planed products are turned into domestic bioenergy in their own pellet factory in Parkano. Wood insulation is also made from the sawdust of planed products. 

The economic downturn 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 developing products in many sectors. We are involved in the development of everything from hot water treatment to lignin. By utilising and improving the natural properties of wood, many new things can still be obtained from it,” Heinonen says.