Organic Mineralisation

The aim of the “Organic Mineralisation” project is to increase the fire resistance of wood (products) through targeted impregnation with halogen-free organic salts that are unproblematic from a toxicological and ecological point of view.


  • Lead school School of Architecture, Wood and Civil Engineering
  • Funding organisation Innosuisse
  • Duration (planned) 01.05.2021 - 01.11.2023
  • Project management Prof. Dr. Thomas Volkmer
  • Head of project Prof. Dr. Thomas Volkmer
  • Keywords Fire retardants, wood modification


Given the UN climate goals (Paris Agreement, 2015), wood is an attractive and particularly sustainable material in that it stores CO2. However, the use of wood as a building material for interior finishing or as a façade element represents an additional fire hazard. This conflicts with the stringent standards that fire protection concepts must meet, especially in public buildings or high-rise construction. Through the use of flame retardants, for example, it is possible to protect wood from combustion and to limit the spread of fire in wood. Inorganic salts have proved their worth in the past, in terms of fire protection. However, being highly water-soluble, they are hard to fix in wood and so cannot be used for outdoor applications. What’s more, many contain halogenated compounds or heavy metals, meaning that the use of inorganic salts must be seen critically from an ecological and toxicological standpoint.

Course of action

The “Organic Mineralisation” project is working on a multivariant process for the two-step impregnation/modification of wood. The gradual introduction of highly water-soluble organic salts results in the precipitation of poorly soluble minerals and thus, the targeted mineralisation of the wood. The in-situ precipitation of poorly water-soluble organic salt compounds can permanently modify the following properties of the wood: • Fire resistance and fire behaviour • Weathering stability (outdoor use) • UV stability • Colour/aesthetic appearance • Sorption behaviour/dimensional stability The salts used are based on organic anions such as oxalates, citrates, acetates, sorbates or formates, as well as the cationic alkali or alkaline earth metals potassium, sodium, calcium or magnesium. The ions can be (relatively) freely combined, enabling the desired changes in the properties of the wood to be implemented in a precise manner according to the particular requirements of a specific application. The requirements depend, to a great extent, on the planned place of application.


Initial results show that different organic salts and salt combinations deliver promising results in terms of their potential as fire retardants. Further large-scale screenings with different salts have revealed which organic salts and combinations are candidates for use in the previously mentioned categories. Their fixation in wood, their ability to absorb humidity from the air and their suitability as a fire retardant were investigated. In initial screenings, salts based on citrates and gluconates turned out to be particularly promising.

Looking ahead

In the next phase of the project, other properties such as weather resistance or mechanical properties will be examined. The project will also seek a solution for the industrial realisation of the products. Besides the process control for treatment with the salts, this also includes a permanent evaluation of the profitability of the various products.