Correct Answer: A. 20%
Solution:
Fungi require certain conditions to thrive and cause decay (rot) in timber. One of the most critical conditions is the presence of sufficient moisture. Fungal growth is typically initiated when the moisture content of the wood rises above the fiber saturation point, which is approximately 20%. Keeping timber seasoned below this level is a key method of preservation.
Correct Answer: B. Bamboo
Solution:
Bamboo is considered a highly sustainable and green building material due to its rapid growth cycle (it's a type of grass), ability to sequester carbon, and renewability. Unlike timber, it can be harvested in a few years. Concrete and brick manufacturing are energy-intensive processes with a significant carbon footprint.
Statement 1: Due to their low strength, particle boards are less durable than plywood or solid wood. However, using laminates or veneers on the surface can aid to improve durability.
Statement 2: A layer of melamine can be applied to the top surface of particle boards to make them fire-resistant.
Correct Answer: A. both statement 1 and statement 2 are true
Solution:
Both statements are correct. Particle boards are generally less durable than solid wood but their surface durability and appearance can be greatly enhanced with laminates (Statement 1). Melamine is a thermosetting plastic that, when used as a laminate, can provide a hard, durable surface with improved fire resistance (Statement 2).
Correct Answer: B. Particle board
Solution:
This question describes the manufacturing process of a particle board. It is an engineered wood product made by pressing wood chips, sawmill shavings, or sawdust and a synthetic resin or other suitable binder, which is then subjected to heat and pressure.
Statement 1: Laminates are the production made by bonding together two or more layers of materials.
Statement 2: High-pressure decorative laminates are pasted on plywood sheets, which are used for large areas like cabinets, wide door shutters, tables, etc.
Correct Answer: B. Both statement 1 and statement 2 are true
Solution:
Both statements accurately describe laminates. Statement 1 gives the general definition of a laminate as a material made by bonding layers. Statement 2 provides a common and correct application of high-pressure decorative laminates, which are widely used as a durable and aesthetic surface for furniture and panels.
Correct Answer: D. Bamboo
Solution:
Trees are classified by their growth pattern. Exogenous trees (like Deodar, Pine, and Oak) grow outwards, forming distinct annual rings. Endogenous trees, on the other hand, grow inwards by adding fibrous mass to their interior. Bamboo is a classic example of an endogenous plant used in construction.
Correct Answer: D. 0°
Solution:
In the flat-pressed or parallel plates process for making particle board, the wood particles are generally oriented parallel to the plane of the board. This means their orientation angle with respect to the plane is 0°. This alignment provides the board with its primary strength and stability along its length and width.
Correct Answer: D. Group A
Solution:
Timbers are often classified into groups based on their structural properties. Group A timber is designated for heavy construction purposes and is characterized by a high modulus of elasticity (a measure of stiffness), typically above 12.5 kN/mm².
Correct Answer: B. Veneers
Solution:
Veneers are thin sheets of wood that are peeled from a log. The most common method for producing veneers is rotary cutting, where a log is rotated against a long, sharp knife, peeling off a continuous sheet of wood, much like unwinding a roll of paper.
Correct Answer: A. Rind gall
Solution:
A rind gall is a type of timber defect characterized by a curved swelling. It forms when a tree heals over a wound, such as one left by the improper removal of a branch. The new growth (sapwood) covers the wound, resulting in this characteristic swollen appearance.
Correct Answer: B. Seasoning
Solution:
Seasoning is the process of drying timber to reduce its moisture content to a level appropriate for its intended use. This is a crucial step as it increases the timber's strength, stability, and resistance to decay, while also reducing its weight.
Correct Answer: C. Heartwood
Solution:
The heartwood is the central, darker, and non-living part of a tree trunk. It consists of the inner annual rings and provides the main structural support for the tree. The sapwood is the outer, lighter-colored living portion, and the cambium is the thin layer of growing cells between the sapwood and bark.
Correct Answer: C. 90°
Solution:
In the extrusion process for making particle board, the wood particle-resin mix is forced through a die. This process causes the majority of the wood particles to align themselves perpendicular to the direction of extrusion, meaning their orientation is at 90° to the plane (face) of the board. This is different from flat-pressed boards where particles are parallel (0°).
Correct Answer: C. Four
Solution:
IS 287: 1993 provides guidelines for the air seasoning of timber. For this purpose, it divides the country into four distinct zones based on average annual relative humidity, which influences the rate and effectiveness of the seasoning process.
Correct Answer: A. Veneer
Solution:
A veneer is a very thin slice of wood, typically between 0.5 mm and 5 mm thick, that is obtained by peeling or slicing a log. Veneers are the fundamental components used to manufacture engineered wood products like plywood and laminated veneer lumber (LVL).