Timber Preservation

Introduction

Timber decay is mainly the result of its being attacked by living organisms such as Fungi and Insects. which require moisture and air to thrive. Even though the timber structure of the Mary Rose was submerged in water for more than 400 years, some 40% has survived because it became covered in mud and silt, which excluded air and prevented organisms from feeding on the wooden hull. It is timber used outside in the open air which is most at risk especially if exposed to excessive moisture. Preservatives work by coating the timber with substances that repel insects and/or will not support living organisms.

Well Seasoned and timber for furniture and interior fittings should be adequately protected by the normal oil, wax, varnish and paint finishes used, provided it remains in a warm dry environment.

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Safety Point! Timber treated with Preservatives should not be burned on open fires or in log burners, since this may release harmful toxins into the atmosphere. Industrial Incinerators work at much higher temperatures such that hazardous compounds are broken down to harmless common elements like carbon, oxygen and hydrogen.

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Naturally Durable Timber

Some timbers are more resistant to decay, or are more Durable, than others. They include Cedar, which is a Softwood and several Hardwoods such as: Teak, Camphor-wood, Oak and Iroko.

Ship's Hulls

Wooden ship hulls were very susceptible to attack by marine organisms , especially in warmer oceans.

Oil-based Preservatives

Creosote is made from distilling Coal Tar. Traditionally, it was used for most external applications (e.g. sheds and fences) but it can cause irritation and has been found to be a health hazard. It was withdrawn from sale to the general public in 2003 but is still available to licenced professional operators. Less harmful substitutes (e.g. Creocote) are now made from petroleum distillates with synthetically manufactured substitutes and are more commonly used. Both these Preservatives are suitable for rough sawn timber and easily applied by liberal application using a brush or by dipping fence posts, for example, and leaving them to soak it in for 20-30mins. They are water repellent and have a strong odour which discourages insects.

Decking Oil is made from Linseed Oil and White Spirit (aka Turpentine Substitute) together with Oil Driers. As the name implies, Decking Oil is used on patio decking and is applied liberally with a brush such that it soaks well into the timbers.

Water-based Preservatives

Structural timbers can also be pressure treated with water borne copper-based preservatives (e.g. Tanalised). The preservative used was ‘Tanalith’ (i.e. Chromated Copper Arsenate (CCA)) but this too is now restricted use because of environmental concerns and is substituted by Chromated Copper Boron (CCB) (ref: TRADA Wood Information Sheet Section 2/3 Sheet 33. Revised June 2005).