Fossilization protects wood against decaying and fire

Garden furnishing made of stonewood. Photo: Lapuan saha
Garden furnishing made of stonewood. Photo: Lapuan saha
Metsäbiotalouden tulevaisuuskuvasto / Forest Bioeconomy Future Catalogue

Lapuan Saha sawmill and Aureskoski wood refining plant have jointly developed so called stonewood designed to create a better resistance against humidity and fire for wood. It is made by covering the wood with a silicate from stone.

’We create a kind of fossilizing process in wood,’ says Kyösti Kurkela, CEO of Lapuan Saha for Rakennusmaailma magazine.

In the process natural stone is converted into liquid silicate under high pressure and temperature. After that the silicate is pressed on wood in a suitable temperature.

After permeating the liquid must be transformed back to solid form. This is made by polymerizing the silicate mostly by using fruit acids. The result of the process is that silicate fills the cell walls but leaves the wood porous. Thermal insulation and breathability of the material is maintained.

The level of saturation may vary depending on the purpose of use of wood. The result of the most thorough saturation is the most strict fire resistant classified wood.

Lighter saturated wood is suited, for example, to terrace wood. The lightest saturation with silicate liquid only on surface can be carried out even at home. In this case only a few millimetres under the surface are protected.

According to Kurkela, this also provides a good protection against rotting. The processing adds the material’s compressive strength and hardness.

Saturating Finnish pine is easy, and costs are not high. The processing does not make the wood brittle, but it sets certain limits for mechanical processing of wood. Stonewood can be sawn and drilled, but planing or sculpting, for example, are not possible.

Because of the effective fire protection of the material, stonewood is not easy to burn in households, for example. It can, however, be burned industrially, turning the material into ashes and sand.

At home, stonewood is safe to bury in the ground after use. According to Kurkela, there are no toxic substances in stonewood. Though rotting may take a long time, says Kurkela.

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