---
title: "Spalling and delamination of concrete"
subject: "Concrete Technology and Masonry Structure"
chapter: 6
key: "semester_5/concrete_technology_and_masonry_structure:spalling-delamination"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/spalling-delamination
site: BCT Engineering
---

# Spalling and delamination of concrete

Concrete Technology and Masonry Structure · Chapter 6: Concrete durability

- Asked in: 2082 Baisakh, 3 marks
- Video: [Concrete Delamination  -  On My Project](https://www.youtube.com/watch?v=Zcfiocb6aIA) — Boys Renovation
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/spalling-delamination
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-6

## Question

Define with suitable schematic diagram spalling and delamination of concrete.

## Short answer

Delamination is separation of cover parallel to the surface at reinforcement level, giving a hollow tap sound. Spalling is the breaking away of concrete chunks from the surface, often following delamination, caused by rust expansion, freeze-thaw, or fire.

## Answer

**Spalling** is the breaking away of pieces of concrete from the surface in the form of flakes or chunks, leaving a rough, shallow cavity. It is caused by corrosion of reinforcement (expansion of rust), freeze-thaw, fire, impact or excess local stress.

**Delamination** is the separation of the concrete cover into thin layers parallel to the surface, at or near the level of the reinforcement, without the layers falling off yet. It is caused by rust expansion of bars, poor finishing (over-trowelling), or fire. The area gives a **hollow sound** when tapped with a hammer, and if it is not repaired it ends in spalling.

```text
 Section through the cover (surface at top, rebar below)

 (a) Sound         (b) Delamination   (c) Spalling
 +-------------+   +-------------+    +----+     +----+
 |    cover    |   |    cover    |    |   \     /   |
 |             |   |- - - - - - -|    |    \___/    |
 |     (o)     |   |     (o)     |    |     (o)     |
 |    rebar    |   |    rebar    |    |   exposed   |
 +-------------+   +-------------+    +-------------+
                    crack parallel     cover has fallen
                    to the surface     off; the rusted bar
                    at bar level       is exposed
```

Delamination (layer parting at bar level) comes first, then spalling (loss of the layer). Repair: remove the unsound concrete, clean the bar, coat it, and patch.

## Check yourself

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

1. What is spalling?
   A. Separation of layers parallel to the surface that stay in place
   B. Cracking pattern of map cracks
   C. Breaking away of flakes or chunks from the surface leaving a shallow cavity
   D. Uniform surface shrinkage
   Answer: C. Spalling is the loss of pieces; causes include rust expansion, fire, freeze-thaw and impact. (Key point: Spalling)

2. How is delamination different from spalling and how is it detected?
   A. Pieces fall off leaving a cavity, giving a ringing sound
   B. It occurs only at the foundation
   C. It is seen only with phenolphthalein
   D. Layers separate parallel to the surface at bar level without falling off, giving a hollow sound on tapping
   Answer: D. Delamination comes first; if not repaired it ends in spalling. (Key point: Delamination)

3. What is the order and repair of delamination and spalling?
   A. Delamination first, then spalling; remove unsound concrete, clean the bar, coat and patch
   B. Spalling first, then delamination; leave unrepaired
   C. They occur together and need no repair
   D. Only paint is needed
   Answer: A. Hollow areas must be removed before patching. (Key point: Order and repair)

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