What is ‘modified’ wood?
‘Modified wood' is a term used to describe timbers that have their natural behaviour characteristics altered by some form of factory pre-treatment. The advantage of this is that sustainable, but not necessarily durable, species can be used without the application of conventional chemical treatments. Modified woods include:
Heat treated timber
Using this technique softwood is heated to a very high temperature which reduces or denatures the natural nutritional content of the wood, the attraction for both fungi and insects. The wood after treatment becomes softer and slightly more brittle, like Western red cedar, but is quite strong enough for cladding. Some processes have been developed which manufacturers claim can minimise the strength reducing affect of the process.
Chemical modification
In this process the wood is impregnated with chemicals that react with the wood substance to change its nature, rendering it more durable and improve moisture resistance and, hence, dimensional stability, and improving the service life of coatings and adhesives. One such method is acetylation which involves pressure impregnation with acetic anhydride, which is derived from acetic acid (vinegar).
For more detailed information about timber cladding, take a look at our book External Timber Cladding, a comprehensive guide to the design and specification of timber cladding.
We also provides a range of services for building designers and product manufacturers to assist with timber cladding queries, as well as training and cpd.
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