About preservation of woods

1. Wood Preservation

2.  The preservation of wood includes painting and other
applied finishes.
 Timber preservation became necessary because
naturally durable timbers became scarce, so ways of
improving the durability of cheaper timbers were
developed.

3. Wood Preservation
 Timber needs to be protected from:
Insects and fungi
Wear and tear
Effects of weathering
 Timber is preserved to prolong the life of the wood and
prevent its natural decay.
 Some timbers are more durable (resistant to decay) than
others, and in general hardwoods are more durable than
softwoods.

4. Preservative types
The main forms of preservative are:
 Tar oil preservatives
 Water borne preservatives
 Solvent-based preservatives.

5. These preservatives can protect the timber in two ways.
1. They give physical protection by stopping fungi and
insects getting at the wood.
2. They give chemical protection, making the wood
poisonous to insects and fungi.
Paint, for example, gives excellent physical protection.

6. Tar Oils
 Normally dark liquids
 Made from coal-tar mixed with chemicals
 Suitable for outdoor use
 Black / Brown colour
 Example: creosote
 Applied by brushing, spraying, dipping or
pressure treatment

7. 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

8. 2: 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
 Chemical protection given
 Uses structural timber and furniture

9. 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

10. 2 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
 Uses furniture and all external woodwork.

11. 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

12. Methods of application
 Without pressure or with pressure.
Brushing
Spraying
Dipping
Pressure Treatment

13. Safety

14.  All preservatives must be handled with care.
 Read any instructions on the container carefully.
 At all times ensure it is safe for use in the room
or house and that it will not harm people,
animals or the environment in any way.
 When working with any chemicals you should
wear all the appropriate protective clothing.
 Remember that safety and care of the
environment also applies to the disposal of
cartons and containers which hold the
preservatives.
Safety

15. Brushing and
spraying

16. Brushing and spraying
 Preservatives can be applied using a brush or a spray
gun. This method is the easiest to use and is not too
costly.
 The preservative, however, doesn't penetrate deep into
the wood and the treatment needs to be repeated
regularly to keep the wood protected.

17. A gate being brushed
with preservative

18. Immersion

19.  The wood is placed into a container of preservative.
 The wood absorbs the preservative over a short time.
 The immersion can be done for a short time (dipping) or
for a longer period (steeping).
 The immersion process penetrates better than brushing
and can be even more effective if the preservative is
heated.

20. Piece of timber being immersed

21. Pressure treatment
 The most effective method of applying preservative is
by forcing the preservative into the wood under
pressure.
 This pressure can come from inside (vacuum) or
outside (pressure).

22.  The timber is put into a treating cylinder.
 The air is sucked out of the cylinder and held for
a few minutes to let all the air come out of the
wood.
 The cylinder is then flooded with preservative
while the vacuum is held. The vacuum is
released allowing the preservative to take the
place of the air in the wood.
 Then pressure is applied forcing the preservative
into the wood.
 A final vacuum is applied for a short time to
remove any excess preservative, this is done so
that no preservative is wasted.

23. Pressure treatment chamber

24. Pressure treatment chamber