•    Timber that is treated with a preservative generally has it applied through vacuum and/or pressure treatment. The preservatives used to pressure-treat timber are classified as pesticides. If left untreated, wood that is exposed to moisture or soil for sustained periods of time will become weakened by various types of fungi, bacteria or insects.
•    Chemical preservatives can be classified into three broad categories: water-borne preservatives, oil-borne preservatives, and light organic solvent preservatives. In more detail these are:

Water-borne:  Water is the most common solvent carrier in preservative formulations due to its availability and low cost. Water-borne systems do however have the drawback that they swell timber, leading to increased twisting, splitting and checking than alternatives.
Oil-borne: These include creosote and they are toxic, have an unpleasant odour and are generally not used in consumer products

Light organic solvents: These have disadvantages due to the high cost and long process times associated with vapour-recovery systems. While this does significantly reduce certain types of emissions, the timber swells during treatment, removing many of the advantages of light organic solvent formulations.

•    New preservation technologies include: glass fortified wood- protects the wood from fire, rot and insect damage. With glass encapsulating the wood fibers, the lumber becomes harder and the strength is increased. Glass wood can be used for in ground contact applications, in water applications and it is Class-A fire retardant. Wood acetylation- Chemical modification of wood at a molecular level has been used to improve its performance properties These include an extended coatings life due to acetylated wood acting as a more stable substrate for paints and translucent coatings. Acetylated wood is non-toxic and does not have the environmental issues associated with traditional preservation techniques.

•    Natural preservation methods include: Tung oil- Has been used as a preservative for wood ships in China for hundreds of years. The oil penetrates the wood, then hardens to form an impermeable layer up to 5 mm into the wood. As a preservative it is effective for exterior work above and below ground, but the thin layer makes it less useful in practice. It is not available as a pressure treatment.

Heat treatments- There is ongoing research as to whether heat treatments can be used to make timber more durable. By heating timber to a certain temperature, it may be possible to make the wood-fibre less appetising to insects. Lower equilibrium moisture, less moisture deformation, and weather resistance. It is weather-resistant enough to be used, unprotected, in facades or in kitchen tables, where wetting is expected.
Mud treatment- wood is only subject to bacterial decay under specific temperature and moisture content ranges, submerging it in water-saturated mud can retard decay by saturating the wood's internal cells beyond their moisture decay range.