---
title: "Defects of timber by natural forces"
subject: "Civil Engineering Materials"
chapter: 7
key: "semester_3/civil_engineering_materials:timber-defects-natural-forces"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/timber-defects-natural-forces
site: BCT Engineering
---

# Defects of timber by natural forces

Civil Engineering Materials · Chapter 7: Timber

- Asked in: 2079 Bhadra, 2 marks
- Video: [Defects in Timber Due to Natural Forces | Timber | Building Materials](https://www.youtube.com/watch?v=VWkPahZDrDs) — SGK Online Education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/timber-defects-natural-forces
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-7

## Question

Explain in brief about the defects in timber due to natural forces.

## Short answer

Natural forces like wind, frost and sun cause defects: shakes (heart, star, cup) from temperature extremes, wind cracks, upsets (crushed fibres), rind galls from branch wounds, burls, twisted fibres, and also callus, water stain and lightning damage.

## Answer

Defects caused by natural forces (wind, frost, sun, lightning or abnormal growth) in the standing tree are:

1. **Knots:** bases of branches enclosed within the wood; they cut across the grain and reduce strength.
2. **Shakes:** heart, star, cup and radial shakes, which are cracks along the fibres due to frost, sun heat, wind or over-maturity.
3. **Wind cracks and upsets:** crushed or broken fibres from strong winds or rough felling.
4. **Rind galls:** swellings where a branch was lost and the bark folded over.
5. **Burls and twisted fibres:** abnormal growths or spiral grain due to constant wind in one direction.
6. **Callus, water stain and lightning damage.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Knots reduce strength because they
   A. Add density
   B. Remove moisture
   C. Cut across the grain and disturb it
   D. Increase hardness
   Answer: C. Disturb grain. (Key point: Knots)

2. Twisted fibres result from
   A. Kiln drying
   B. Fungus
   C. Sawing
   D. Constant wind in one direction causing spiral growth
   Answer: D. Wind-induced spirality. (Key point: Twisted fibres)

3. Shakes are
   A. Cracks along fibres due to frost, sun heat, wind or over-maturity
   B. Fungal stains
   C. Sawing marks
   D. Seasoning checks only
   Answer: A. Heart, star, cup and radial. (Key point: Shakes)

## Related in Civil Engineering Materials

- [Defects of timber](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Adefects-of-timber) — Civil Engineering Materials, chapter 7, asked 4×
- [Defects caused by seasoning](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aseasoning-defects-timber) — Civil Engineering Materials, chapter 7
- [Defects during growth phase of trees](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Atimber-defects-growth-phase) — Civil Engineering Materials, chapter 7
- [Natural versus artificial seasoning](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Anatural-artificial-seasoning) — Civil Engineering Materials, chapter 7

## Related in other subjects

- [Damp proofing and defects due to moisture](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Adamp-proofing-defects) — Building Technology, chapter 1
- [Types of timber and its defects](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Atimber-types-defects) — Design of Steel and Timber Structure, chapter 9
- [Truss: bar forces due to load and temperature](https://www.bctengineer.com/question.md?key=semester_5%2Ftheory_of_structures_ii%3Atruss-load-and-temperature-9kn-18kn) — Theory of Structures II, chapter 2
- [Acoustics, acoustic defects and remedies](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aacoustics-defects-remedial) — Building Technology, chapter 1