Lignisol is a light, soft building block made of wood fibres bound with lignin. The material was used in the middle of the twentieth century as an insulating, non-loadbearing block, among other places in cavity walls and in cold stores and frost-free storage buildings.
Lignin is the natural binder that holds the fibres together in wood. By processing wood fibres under heat and pressure, that lignin can serve as a binder again — without adding cement or synthetic resin.
Properties
- Light. Because of the high wood content and open structure, the block weighs a fraction of a fired brick or concrete block.
- Insulating. The air trapped in the fibre structure slows both cold and heat. At a time when insulation material was not yet a given, that was the main argument for using it.
- Soft and easy to work. Cut with hand tools, which makes fitting around pipes and irregularities straightforward.
- Moisture sensitive. This is the key limitation. The material takes up water readily. In a damp environment it loses its insulating value, and sustained moisture leads to decay and mould.
Use
The block was not intended to carry load. It was used as:
- cavity fill or inner leaf in a cavity wall, with the outer leaf keeping driving rain out;
- an insulating partition in buildings where a temperature difference mattered, such as stores that had to stay frost-free;
- a thermal break where a cold bridge had to be avoided.
Where you meet it now
Lignisol is not a material you can buy today. It is a historic trade name from a generation of light, organic building materials that has since been replaced by mineral wool, EPS, PIR and modern wood-fibre insulation boards. Those modern boards work on the same principle, but are better protected against moisture and have a documented, certified insulation value.
If you meet the material while renovating a house from the 1940s to 1960s, bear in mind:
- Do not count on its insulation value. After decades in a cavity the original performance is usually gone, certainly if moisture has ever reached it.
- Check for moisture damage before closing the cavity or retrofitting insulation. Saturated, decayed material has to come out, or you insulate moisture in.
- Do not treat it as loadbearing in a structural calculation.
- In a house of that period, asbestos in other building elements is a real concern. Lignisol itself contains no asbestos, but if there is doubt about adjacent boards or mastics, have a survey done before demolition starts.
Related terms
- Wood-wool cement board
- Wood fibre board
- Cavity wall
- Cavity insulation
- Lignin
- Thermal bridge
- Insulation value
Want to know more about building terms? Take a look at our knowledge base on fredsdiyplans.com.