Due to attack of dry rot, the timber ..........
Fungal Decay in Timber: Dry Rot
Dry rot is a type of wood decay caused by a specific group of fungi that break down the cellulose and hemicellulose in wood, which are the components that give wood its strength. Despite its name, dry rot requires moisture to begin (typically >20% moisture content). It thrives in damp, unventilated conditions. Once established, some dry rot fungi can even transport water to dry areas, allowing the decay to spread.
📝 Detailed Analysis of the Options
(a) cracks
While severe dry rot can cause the wood to crack in a distinctive cubical pattern, cracking is a secondary effect. The primary action of the fungus is decomposition, not just cracking.
(b) shrinks
Shrinkage is primarily caused by the loss of moisture during seasoning, not by fungal attack. While the decayed wood may lose volume, the defining characteristic of the decay is the change in substance, not just size.
(c) reduces to powder
This is the correct answer. The defining characteristic of dry rot is the way the fungus consumes the structural components of the wood. As the cellulose is broken down, the wood loses all its strength and cohesion. It becomes dry, brittle, and is easily crushed into a fine, brown, crumbly powder. This powdering is the final stage of the decay process and the most accurate description of its effect.
📊 Dry Rot vs. Wet Rot
| Feature | Dry Rot | Wet Rot |
|---|---|---|
| Final State | Dry, brittle, reduces to brown powder | Soft, spongy, may feel wet |
| Moisture Needed | Needs moisture to start, can spread to dry wood | Needs continuous high moisture |
| Fungal Growth | May have large, fleshy fruiting bodies and fine white strands | Typically has dark, thread-like strands |
💡 Study Tips
- Dry Rot = Dry Powder: This is a direct and easy way to remember the outcome. The name "dry rot" describes the final state of the decayed wood.
- Fungus Eats Wood: Think of the fungus as literally eating the wood's fibres, leaving behind a useless, powdery residue.
- Ventilation is Key: Remember that dry rot thrives in stagnant, damp air. Good ventilation is one of the best ways to prevent it.