Alternative method

• Careful attention to roofing and flooring details and ventilation . 
• Avoid timber to contact brick or concrete (eg use impervious seprating membrane ) .
• Careful maintenance of roofing and guttering
• Apply anti-termite solution at the beginning of construction . 
• Painting to timbers are done properly 
• Chemical treatment to all timber before construction . 
• Select timbers and sent for chemical treatment test as often as possible ( usually , 25mm all-round penetration is required ) . 

Diffusion process

• Freshly converted green timber with high moisture content more than 50 percent is dipped into concentrated boron solution . 
• Timber is covered to prevent evaporation and left for months for solution to diffuse throught timber . 
• Timber is then seasoned . 

Application methods

Selection of techniques to apply preservation is important . Otherwise , preservation may not penetrate into timber sections . The followings are various techniques :

• Brushing or spraying . 

1. Limited penetration 
2. For in situ remedial work 
3. Require several coats . 

• Dipping 

1. Immersion in preservative for a period . 
2. Open tank method - preservative heated then cooled while timber is submerged to get better results . 
3. Not suitable for hardwoods or low-permeability softwoods . 

• Double vacuum process 

1. Vacuum is applied to timber in sealed chamber . 
2. Preservative is introduced . 
3. The vacuum released , forcing preservative into wood . 
4. After a soaking period  ,vacuum is reapplied to eject excess preservative . 
5. Widely used for organic preservatives for external joinery such as window frames . 

• Pressure impregnation 

1. Used for water based and tar oil preservatives 
2. Air surrounding timber is compressed , preservatives introduced under high pressure forcing it into timber . 
3. Expensive . 
4. Longer to dry 
5. Good protection .

Boron Diffussion

• Freshly felled timber is dipped into concentrated borate solution which diffuses throughout the wood by means of its own moisture . 
• Advantage on difficult timbers - which do not readily admit preservatives .

Types of preservatives

1. Tar oil Edit HTML

• Eg creosotes 
• Very effective 
• Derivative from wood or coal
• Suitable for external use due to noticeable colour and smell and causing timber unsuitable for painting . 
• Cheap , can be applied to timber with fairly high moisture content . 
• Reduce rate of weathering . 
• Creep into porous adjacent materials such as cement rendering and plaster . 
• Water-borne 

 Water-borne

• Consist of salts based on metal such as sodium , magnesium , zinc , copper , arsenic and boron . 
• Eg copper chrome arsenate (CCA) 
• Copper - fungicide , arsenate - insecticide 
• Very tolerant of moisture in timber , odourless , non-flammable , non-creeping , do not stain timber , may be painted on drying out 
• Fairly cheap 
• Disadvantages - swell the timber , cause corrosion of metal in contact . 
• Used as preliminary protection followed by kiln drying . 

Organic Solvent

• Organic fungicides / insecticides such as lindane , metallic napthanates and pentachlorophenol in volatile organic solvents . 
• Penetration is excellent on dry timber . 
• Brush or spray application . 
• Non-creeping , non - staining , non -corrosive to metals , non-swelling and quick drying . 
• Flammable , fire-risk until dried . 
• Expensive .
• Contain high volatile organic compound (VOC) could be hazardous to health . Require care in handling .

Boron diffusion

• Freshly felled timber is dipped into concentrated borate solution which diffuses throughout the wood by means of its own moisture . 
• Advantage on difficult timbers - which do not readily admit preservatives .

Prevention of timber

• Timber is preserved to protect from attack of insects and from internal decay due to rots . 
• Good seasoning is the most effective mean of preservation . 
• Preservatives should be toxic to fungiand insects , chemical stable , able to penetrate timber and non-aggressive to surrounding materials , eg metals aggressive to surrounding materials , eg metal . 
• Various types of preservatives available . 
• Before applying preservative , timber should be well-seasoned other wise pores in timber will be blocked , causing decay due to entrapped moisture .

prevention

Requirement for growth - Prevention

• Suitable food ie timber especially sapwoood - preserve timber 
• Moisture at least 20 - maintain low moisture content ( seasoning ) 
• Suitable temperature about 23 celcius - lower than 0 or higher than 38 celcius . 
• oxygen  - seal timber ( example paint ) .