Chemicals that do not swell timber such as petroleum oils and creosote have no appreciable affect on timber properties. Timber-swelling chemicals such as water, alcohol and some other organic fluids do not degrade the timber but may lower mechanical properties. When these liquids are removed, swelling will be reversed and mechanical properties regained.
Timber is resistant to mild acids. However strong acids (pH less than 2) and strong alkalis (pH greater than 10) can cause degradation of the chemical components of timber. The degree of degradation is dependent upon many factors including species of timber (softwoods are more resistant to attack by acids and alkalis than hardwoods), type of chemical (oxidising acids are worse than non-oxidising) and exposure conditions.
Some softwoods such as cypress pine are highly resistant to a wide variety of chemicals in reasonable concentrations at ambient temperatures and are widely used for chemical storage and processing.
Examples of timber applications where resistance to chemical attack is of benefit include:
- waste landfill piling (usually acidic);
- tanneries;
- vats;
- piles or fascines in swamps;
- enclosed swimming pool buildings;
- chemical storage buildings and
- water treatment works;
Since many variables are involved in adverse chemical environments, industrial sources should be contacted for specific advice.
For special situations where chemical degradation is of concern, the natural chemical resistance of timber can be further enhanced by impregnation with:
- phenolic resins (improves acid resistance);
- furfuryl alcohol (increases alkaline resistance) and
- monomeric resins followed by polymerisation (greatly improves chemical resistance).
Reference: Timber Datafile P4 – Timber – Design for Durability of the NAFI Timber Manual.
