Timber treatment process

A number of chemical brands and technologies are available for pressure treated timber, below is a list of the common timber treatment technologies used for protection against biological decay.

Copper-organic (water-based)

Use class suitability: UC1, 2, 3 and 4.
Application process:  high-pressure

Suitable for situations were a risk of bio-deterioration is high, e.g. ground and fresh water contact components, fencing, decking, timber embedded in masonry.  Treated wood has no smell and does not discolour or taint adjacent materials.  Treatment imparts a greenish colour to the wood making it easy to identify.  A dye can be added to give a brown colour.  Treatment will cause wood to swell, raise the grain and may cause some distortion.

Organic (water-based)

Use class suitability: UC1, 2 and 3 (uncoated and coated)
Application process: high-pressure

Ideal for external, out of ground contact landscape and cladding timbers. Treatments are clear and do not colour the wood. A colourant can be added to aid identification. Treatment will cause wood to swell, raise the grain and may cause some distortion.

Microemulsions (water-based)

Use class suitability: UC1, 2 and 3 (coated).
Application process: low pressure (double vacuum)

Ideally suited for internal construction timbers. Although water-based, the treatment has little effect on dimensions of timber but may raise the grain. Can be used for joinery items where surface appearance is not of prime importance.

Biological Treatment preservatives and processes -Pressure Andrew Goto
Timber Treatment tank

Organic solvent (also known as light organic solvent products LOSP)

Use class suitability: UC1, 2 and 3C (coated)

Application process: low pressure

Organic solvent preservatives do not change the dimensions of timber or raise its grain; they do not change the colour of the timber (unless tinted for the purposes of identification), making them particularly suitable for joinery products.

Boron compounds

Use class suitability: UC1, 2 and 3C (coated).
Application process: high-pressure processes to seasoned timber alternatively, by diffusion processes to timber before seasoning.

Boron treatments do not change the colour of the timber. Treatment may raise the grain and, if applied using a high-pressure process, may cause the timber to swell.

Creosote

Use class suitability: UC3u (uncoated), 4 and 5
Application process: high pressure

Buying well pressure treated timber- biological preservation-BS8417

How to Specifying treated timber

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