Fire retardant process

Fire retardant process Autoclave

Autoclaved fire retardant timber


Lumbers are put into a specific vacuum-pressure device called autoclave. The flame retardant agent will be imprgnated in the whole piece of wood down to the core.

Wooden elements are first stacked in a specific way (pic.1), then impregnated with fire retardant water-based agent (pic.2 sqq.) and eventually kiln-dried until they reach the suitable required humidity.


Impregnation of wood


Wooden elements are soaked under pressure with a water-based solution containing active salts (pic.2 & 3) which effect will be to decrease the capacity of wood to ignite and spread the fire. This process can be lead onto lumbers which have been correctly dried prior to this action.


To ensure the active agent is evenly spread into every piece of wood and maximise its efficiency, Woodenha uses a patented stacking technique and monitors the whole process throughout all of its duration. Each piece is then weighed to mark the quantity of active agent kept inside. The fire retardant product is colorless,odourless, inorganic and does not contain VOC.


The material is deeply impregnated with the flame retardant agent (pics. 4,5 & 6). This reveals to be a very efficient and durable process which gives the treated wood a good fire reaction, in most of the cases Euroclass B is given.


Impregnation tends to roughen the surface of wood as the fibers may go up a little; this process might then need a sanding work especially when a coating is to be applied afterwards. The coating - varnish, paint or stain - must not degrade the fire reaction.


Kiln drying


In order to stabilize the active salts inside the timber and get rid of water from it, they must then be kiln dried until they reach the suitable percetage of humidity required for the purpose. This is the second kiln-drying of the timber, and it must be carefully monitored to avoid dimensionnal and stability issues and minimize color dying. Woodenha must be notified of the final use of the timber and the required humidity prior to commencing the fire retardant process, according to the leagl building standards.

After KD, timber may now be coated with a non-degrading varnish, paint or stain

Troughout the process, a set of control measures is made; Woodenha can deliver retention rate and final humidity for every batch of autoclaved wood as mentionned our tracking and quality policies.



Download technical litterature on Woodenha's fireproof process.



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