POTENTIAL TIMBER DEFFECTS AND TREATMENT pptx

The topic deals with defects of timber and how timber could be protected from fungi, termites and insects

1. TIMBER DEFECTS A ‘defect’ is generally an imperfection, which either weakens the wood greatly or makes the wood unsuitable to work with. There are sources of defects in timber. These are grouped into the following categories; Defects due to conversion Defects due to fungi Defects due to insects Defects due to natural forces Defects due to seasoning

2. Preservation and protection of timber Timber species need a form of protection to withstand the test of time against the following: Wood-destroying fungi Wood-destroying insect Termite Dirt and dust Fire

3. This protects can be achieved through preservative treatment with chemicals, a protective media (in the form of varnishes or paints) and through appropriate construction details (which will help keep off the causes of harm). Insects: Wood is attacked by pinhole borers in both hardwood and sapwood of the log, and later by powder post beetles during and after seasoning.

4. Termites: There are two types of termites which cause damage to wood, the subterranean or soil termites which live in the soil and find their way into buildings in their search for food and widely spread through the tropics. The dry wood termites which live inside wood tend to concentrate in the coastal regions. Fungi: These are low form of plants which digest the wood on which they grow. In order to grow they need temperature of 5 to 30°C, an adequate supply of oxygen and moisture content in their environment.

5. Protection against insects, termites and fungi is achieved through application of preservatives. Some of these are : Brushing or spraying T his is a non-pressure method of application which should be used only on well-seasoned timber. Penetration is poor, usually only about 1 to 2mm deep. Dipping This method is more effective than brushing since there is certainty that the preservative reaches all surfaces of members which have been cut to shape prior to the treatment.

6. Immersion T his open tank treatment gives good protection to permeable timbers. In this treatment the timber is submerged in a tank of preservative and heated for several hours and allowed to cool for the preservative to be completely absorbed into the species. Pressure impregnation This is probably the best and most effective method of preservative application. It is a combined use of pressure and heat to gain complete penetration of permeable and some penetration of resistant timbers.

7. Preservative qualities There are certain requirements a good preservative must fulfill, it should be: Toxic to fungi, insects and termites, but not to human or animals Permanent after application with no leaching out. Non corrosive to metals Capable of accepting subsequent painting Colourless and odourless . Safe to handle and easy to apply. Non-flammable .

8. Types of preservatives Tar oil: The well-known preservative of this type is coal tar creosote. Tar oils are very resistant to leaching. They prevent checking, splitting and also assist in preventing the ingress of fungi spores into the timber. They are also not corrosive to metals. Their disadvantage is that they are difficult to paint over.

9. Types of preservatives b) Organic solvent: These preservatives are soluble in organic solvent. They are suitable for both exterior and interior use because of their resistant to leaching. They can be painted over; they do not stain and are non-corrosive to metals but very expensive.

10. Types of preservatives c) Water-borne: These are salts such as Copper, Chromium, and arsenic, Zinc, Mercury, Sodium and Potassium which are dissolved in water to give a toxic solution. They are usually odourless and can be painted over after drying.

11. Wood base material Wood products used in construction can be classified under two main headings. Structural timber: These are load bearing walls frames, floors, columns, beams and roof trusses. Non-structural timber: These are timber elements which are non-lad bearing. They are used for internal walls and partitions, windows, doors and finishes.