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Wood Preservation

Wood Preservation. Wood Preservation. Timber needs to be protected from: Insects and fungi Wear and tear Effects of weathering Main types of preservatives: Tar oils Water-borne preservatives Solvent based preservatives. Tar Oils. Made from coal-tar mixed with chemicals

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Wood Preservation

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  1. Wood Preservation

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

  3. Tar Oils • 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

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

  5. Water-Borne Preservatives • 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

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

  7. Solvent Based Preservatives • 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

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

  9. Methods of application • Number of different methods: • Brushing • Spraying • Dipping • Pressure Treatment

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

  11. Pressure Treatment • 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

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