---
title: "Reasons for cracks in plastering"
subject: "Building Technology"
chapter: 9
key: "semester_6/building_technology:plaster-crack-reasons"
source: https://www.bctengineer.com/q/semester_6/building_technology/plaster-crack-reasons
site: BCT Engineering
---

# Reasons for cracks in plastering

Building Technology · Chapter 9: Finishing works

- Asked in: 2078 Baisakh, 2 marks
- Video: [Plaster cracks | Reason of cracks in plaster](https://www.youtube.com/watch?v=Q6544DJPIlc) — Online Mistry
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/plaster-crack-reasons
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-9

## Question

What are the reasons behind development of cracks in plastering?

## Short answer

Plaster cracks are caused by shrinkage of rich mortar or poor curing, use of fine or clayey sand, and insufficient bond to a dry or smooth background. Structural movement, differential expansion at brick-concrete junctions without mesh, single-coat thick application, and rapid drying also lead to cracking.

## Answer

Cracks in plastering arise from:

- **Shrinkage** of rich cement mortar (too much cement or water) or poor curing.
- **Poor quality sand** (too fine or with clay and silt).
- **Poor bond** to the background, dry or dusty wall, or smooth surface without a key.
- **Movement** of the structure: settlement, thermal and moisture movement of the wall or frame.
- **Different materials** meeting at one surface (brick and RCC) without mesh or a joint.
- **Excess thickness** applied in a single coat.
- **Premature drying** from sun and wind.
- **Vibration, overloading, or structural cracks** passing through the plaster.

## Check yourself

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

1. Which cause cracks via shrinkage?
   A. Fine brick
   B. Painting
   C. Rich cement mortar, excess water or poor curing
   D. Lean sand
   Answer: C. Too much cement or water shrinks. (Key point: Shrinkage)

2. Why crack where brick meets RCC?
   A. They bond
   B. Same expansion
   C. Colour difference
   D. Different materials move differently without mesh or joint
   Answer: D. Differential movement cracks the plaster. (Key point: Different materials)

3. Which causes cracks in a single coat?
   A. Excess thickness
   B. Thin coat
   C. Curing
   D. Wetting
   Answer: A. Thick single coats shrink and crack. (Key point: Thickness)

## Related in Building Technology

- [RWH: reasons and basic components](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Arwh-reasons-components) — Building Technology, chapter 12

## Related in other subjects

- [Reasons for I/O interfaces](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aio-interface-reasons) — Computer Organization and Architecture, chapter 7