4.2B Timber

4.2B Timber

Essential idea here is that materials are classified into six basic groups on their different properties.

Hardwood and softwood

Softwoods 

• come from coniferous trees which are evergreen, needle-leaved, cone-bearing trees and grown in temperate regions.

Hardwood 

• come from deciduous trees which are broad-leaved or Angiosperm trees which are both seed bearing.

Characteristics of natural timber

• Tensile Strength:                                                                                                                                     -The tensile strength of natural timber is greater along the grain than across the grain.
• Resistance to damp environments:                                                                                                         -Very resistant.
• Longevity:                                                                                                                                             -Hardwoods very good. Softwoods good.
• Aesthetic properties:                                                                                                                               -Natural colours range (red, purple, cream and brown).                                                                 -The grain can add to its aesthetics.
• Resistance to damp environments:                                                                                                        -Very resistant.

Man-made timber

• Manufactured boards are timber sheets which are produced in gluing wood layers or wood fibres together.
• Often made of waste wood materials.
• Can be made in very large sheets of consistent quality.

MDF

• Smooth, even surface. Easily machined and painted or stained. Also, available in water and fire resistant forms.
• Used mainly for furniture and interior panelling due to its easy machining qualities. Often veneered or painted. 
• Resistance to warping. 
• Have a layered structure, which makes fixing to the edges difficult. 
• Commonly for furniture.

Plywood 

• Very strong board which is constructed of layers of veneer or piles which are glued at 90 degrees to each other.  
• Very strong in all direction, as it cannot split along the grain like timber.

Chipboard/Particle board 

• Made from chips of wood glued together. Usually veneered or covered in plastic laminate. 

Characteristics of man-made timber

·       Tensile strength: depends on the man-made timber

o   Plywood – high tensile strength in all directions

o   Particle board and MDF – very low

·       Resistance to damp environments: depends on the man-made timber.

o   Exterior plywood – excellent.

o   Interior plywoods - very low

o   Particle board and MDF – very low

·        Longevity:

o   Plywood is high

o   Particle board and MDF is low to medium

·       Aesthetic properties:

o   Plywood if the top layer is of a nice timber like Beech will be good

o   Particle board and MDF requires finishing or a sheet of lamination (see previous section)

Treating and finishing timbers

This process reduce the moisture content so that if becomes workable. The remaining moisture, albeit small, means that the wood never really stabilise and continues to swell and shrink, with humidity and temperature.
Timber treatments & finishes are used to protect, enhance and improve the mechanical properties. 


Timber treatments: 
Preservative to improve the timber's resistance to attack and improve its durability is enhanced to a level which is suitable for the intended use.

• Wood destroying fungi - resulted from moisture 

• Wood destroying insects - borers, white ants 

Timber finishes: 

Carried out to achieve one or both of the following reasons: 

• Aesthetics - improve the materials natural beauty 
• Function - protect it from environment impact, heat, moisture

Recovery & disposal of timber

• Wood recycling is the process of turning waste timber into usable products. 
• Timber is one of the most renewable and 'earth friendly' materials available.
• Recycling timber is a practice that was popularised in the early 1990s as issues such as deforestation and climate change, prompted both timber suppliers and consumers to turn to a more sustainable timber source.
• Recovery                                                                                                                                               -Timbers can be reused and recycled so that they can last longer but this involves using                more chemicals and materials. This usually happens with expensive woods and                          hardwoods only.
• Disposal                                                                                                                                                 -Timbers are usually disposed at landfills and are left to rot and break down.                               -Timbers with chemicals usually cause more problems as they can affect the environment            if not disposed of properly.