---
title: "Crazing and cracks on roof"
subject: "Building Technology"
chapter: 10
key: "semester_6/building_technology:crazing-roof-cracks"
source: https://www.bctengineer.com/q/semester_6/building_technology/crazing-roof-cracks
site: BCT Engineering
---

# Crazing and cracks on roof

Building Technology · Chapter 10: Causes and prevention of cracks in buildings

- Asked in: 2081 Chaitra, 4 marks
- Video: [DIFFERENCE BETWEEN PLASTIC SHRINKAGE CRACKS & CRAZING CRACKS](https://www.youtube.com/watch?v=w_vZZ4Ia0rY) — 𝐁𝐥𝐨𝐨𝐦 𝐰𝐢𝐭𝐡 𝐀𝐧𝐚𝐦𝐢𝐤𝐚
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/crazing-roof-cracks
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-10

## Question

Define crazing. What are the common problems for crack on roof of the building?

## Short answer

Crazing is a network of fine, shallow surface cracks caused by rapid drying, rich mix, or over-trowelling. Common roof crack problems include thermal expansion and contraction of slab and parapet, shrinkage from poor curing, deflection, reinforcement corrosion, differential movement, and lack of expansion joints or waterproofing.

## Answer

#### Crazing
**Crazing** is the formation of a network of fine, shallow, hair-like cracks on the surface of plaster, concrete, paint or glaze, looking like a spider web or map. It is caused by shrinkage of the surface layer due to rapid drying, rich mix, too much trowelling, or sudden temperature change. It affects appearance only and is repaired by filling with cement slurry or repainting.

#### Common problems of cracks on roofs
- **Thermal expansion and contraction** of a slab or parapet in sun, causing cracks and leaks.
- **Shrinkage cracks** in the terrace screed or slab due to poor curing.
- **Deflection and overload** causing cracks in slabs.
- **Corrosion of reinforcement** with spalling at the soffit.
- **Differential movement** of the parapet and slab causing horizontal cracks.
- **Poor waterproofing** and ponding, giving leakage and dampness.
- **Lack of expansion joints** in large terraces.

**Prevention:** good curing, expansion joints, insulation and waterproofing, correct slope, proper reinforcement cover.

## Check yourself

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

1. Crazing is:
   A. A wide diagonal structural crack
   B. A network of fine shallow hair-like cracks on a surface
   C. Settlement of foundation
   D. Corrosion of bars
   Answer: B. It looks like a spider web or map. (Key point: Definition of crazing)

2. Crazing is caused by:
   A. Overloading
   B. Earthquake
   C. Shrinkage of surface layer due to rapid drying or excess trowelling
   D. Root growth
   Answer: C. Rapid drying, rich mix and over-trowelling shrink the surface. (Key point: Cause of crazing)

3. Which helps prevent roof cracks?
   A. Ponding of water
   B. Removing slope
   C. Poor cover
   D. Good curing, expansion joints and waterproofing
   Answer: D. Curing, joints, insulation and waterproofing are the preventive measures. (Key point: Roof cracks)

## Related in Building Technology

- [Common problems of existing foundations](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aproblems-existing-foundation) — Building Technology, chapter 2, asked 2×
- [Causes of cracks in a building](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acauses-of-cracks) — Building Technology, chapter 10, asked 3×
- [Horizontal crack below RCC slab](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ahorizontal-crack-below-slab) — Building Technology, chapter 10
- [Structural and non-structural cracks](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acracks-structural-nonstructural) — Building Technology, chapter 10, asked 4×
- [Methods of repairing cracks](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acrack-repair-methods) — Building Technology, chapter 10, asked 3×
- [Causes and remedies of cracks](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acracks-causes-remedial) — Building Technology, chapter 10, asked 2×

## Related in other subjects

- [Wind pressure on sloping roof, Delhi](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Awind-sloping-roof-delhi-10m) — Design of Steel and Timber Structure, chapter 8, asked 3×
- [Wind pressure on sloping roof, Madras](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Awind-sloping-roof-madras) — Design of Steel and Timber Structure, chapter 8, asked 3×