Wood Preservation Wood Preservation n Timber needs to

Wood Preservation

Wood Preservation n Timber needs to be protected from: ¨ Insects and fungi ¨ Wear and tear ¨ Effects of weathering n Main types of preservatives: ¨ Tar oils ¨ Water-borne preservatives ¨ Solvent based preservatives

Tar Oils n n n Made from coal-tar mixed with chemicals Suitable for outdoor use Black / Brown colour Example: creosote (ESB poles) Applied by brushing, spraying, dipping or pressure treatment

Tar Oils n Advantages ¨ Toxic to fungi and insects ¨ Easily absorbed by the wood ¨ Long lasting ¨ Inexpensive n Disadvantages ¨ Strong smell ¨ Toxic to plants ¨ Difficult to paint over

Water-Borne Preservatives n n n Made from mixture of toxic salts(copper and zinc) and water When applied to wood, water evaporates leaving toxic salts to act as preservatives Usually pressure impregnated

Water-Borne Preservatives n Advantages ¨ Colourless ¨ Odourless ¨ Can be painted over n Disadvantages ¨ Timber needs to be dried out by a kiln after treatment ¨ Can cause swelling ¨ Salts can be washed out from the wood

Solvent Based Preservatives n n n Made from toxic chemicals dissolved in a liquid other than water (usually white spirits) After treatment the solvent evaporates, leaving the preservative in the wood Can be applied with a brush or with a spray gun

Solvent Based Preservatives n Advantages ¨ Resistant to leaching ¨ Can be painted over ¨ Can be used indoors n Disadvantages ¨ Have a strong smell ¨ Can be a fire hazard ¨ Expensive

Methods of application n Number of different methods: ¨ Brushing ¨ Spraying ¨ Dipping ¨ Pressure Treatment

Methods of application n Brushing and Spraying ¨ Easiest to use, not too costly ¨ Does not penetrate wood deeply, only coats the outer surface n Dipping ¨ Wood is dipped into a tank of preservative ¨ Wood soaks in the preservative quickly

Pressure Treatment n n n Most effective and expensive method Preservative is forced into the wood by pressure Wood is placed in a chamber, air is sucked out creating a vacuum, preservative is pumped into the chamber and the vacuum is released. Pressure is applied to force preservative to enter wood cells Final vacuum is applied for a short period to remove any excess preservative Length of time the vacuum is released depends on the permeability of the wood