Understanding Wood: Properties, Protection, and Uses
Wood: An Overview of Properties and Uses
Wood’s strength and flexibility depend on the direction of its fibers. As an organic material, its lifespan is shorter compared to other materials.
- Advantages: Easy to use, suitable for temporary structures, easy to transport, low density, easy to work with, lightens structures, provides thermal and acoustic insulation.
Disadvantages: Susceptible to fungi and insects, not an inert material, swells with water, prone to premature aging, can rot and is vulnerable to fire. Natural light penetration is limited to 5 meters in open spaces. Alternating moisture and drying can cause negative effects.
Wood Properties
Wood properties differ in axial, radial, and tangential directions.
Physical Properties
Physical properties are influenced by humidity and fiber direction.
– Specific Gravity: Varies slightly between real and apparent, influenced by moisture.
– Thermal Properties: The thermal expansion coefficient is very small, and expansion is offset by moisture loss from heat. Thermal conductivity depends on the wood type and increases with weight. It’s higher in the axial direction, but the air inside provides thermal insulation.
– Electrical Properties: Dried wood is a good electrical insulator, though resistivity decreases with increasing temperature. It depends on the species, bulk density, and direction, being 2 to 4 times greater in the axial direction than transverse. Resistivity increases with specific gravity and is greater in species with resins and oils.
Durability
Resistance to destructive agents depends on natural or artificial antiseptics and the absence of nutrients for these organisms. Site conditions also affect moisture, especially alternating with dryness. Wood can last for centuries in fresh water. Contact with the ground is another factor, resisting well in clay but deteriorating in sandy and limestone soils.
Mechanical Properties
Anisotropy is a significant factor.
– Hardness: Wood is generally a soft material. Hardness is proportional to the square of its density and decreases with moisture. Within the same type of wood, heartwood is harder than sapwood, and older wood is harder than younger wood. There’s no difference between transverse radial or tangential surfaces.
– Resistance: Workability increases with straightness of fibers and compactness, and can be expressed in terms of humidity.
Wood Protection
Take appropriate measures to prevent damage after production. If wood isn’t severely damaged, proceed with curing.
Phases of Wood Processing
- Dismounted and Diverted: Cutting and removing sap, done by washing and water vapor.
- Drying: Removing moisture to stabilize the wood, prevent fungal growth, and increase resistance. Drying can be artificial or natural.
- Artificial Aging: Artificial drying is stronger, removing nearly all moisture.
- Use of Protectors: Chemicals that make wood more resistant to destructive agents.
Wood Processing
- Tree felling and transportation to the sawmill.
- Splitting the wood into boards, planks, etc.
- Creating commercial forms of wood.
Types of Wood for Construction
- Plywood: Odd number of plates with fibers perpendicular to contiguous layers. Used in cabinetry.
- Glulam: Similar to plywood, but fibers go in the same direction, resulting in less resistance.
- Compressed Wood: Compressed to eliminate voids, creating a compact and durable material.
- Metallic Wood: Immersed in liquid metal.
- Flake Board: Wood waste is compressed and glued, offering little resistance.