---
title: "Random rubble and dry rubble masonry"
subject: "Building Technology"
chapter: 3
key: "semester_6/building_technology:random-dry-rubble"
source: https://www.bctengineer.com/q/semester_6/building_technology/random-dry-rubble
site: BCT Engineering
---

# Random rubble and dry rubble masonry

Building Technology · Chapter 3: Mortars & Masonry works

- Asked in: 2077 Chaitra, 4 marks
- Video: [RUBBLE WORK DETAILS, DR MASONRY-RR MASONRY | What is DR and RR in Stonework?](https://www.youtube.com/watch?v=G9vkg3_ecDs) — HANUKKAH HOMES
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/random-dry-rubble
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-3

## Question

Describe random rubble and dry rubble masonry with figure.

## Short answer

Random rubble uses irregular stones bedded in mortar, with through stones at about 1.5 m spacing for bonding. Dry rubble lays stones without mortar, relying on interlocking and weight; it allows free drainage and is used for retaining and boundary walls.

## Answer

#### Random rubble masonry
Rough, irregular stones, in the shape in which they come from the quarry, are laid without any definite courses. Mortar (1:6 cement-sand or lime) fills the gaps, and smaller stones fill the voids. Through (bond) stones are placed at about 1.5 m spacing to bond the full thickness of the wall. The minimum wall thickness is about 400 mm.
- **Uncoursed:** no courses at all; cheapest.
- **Coursed:** brought to a level at every 300-350 mm height, forming rough courses.

```text
    ___ ____ __ ___
   /   \    \  \   \   irregular stones, thick
  /__ __\____\__\___\  and irregular joints
  \  /  /   /\   /
   \/__/___/__\_/
```

#### Dry rubble masonry
Rubble stones are laid **without any mortar**; stability depends on proper interlocking and the weight of the stones. Large stones are used at the bottom, and bond stones are placed across the thickness.
- Stones are carefully selected and fitted; small stones (chinking) are wedged into the gaps.
- The wall thickness is large (about 600 mm at the base) and the height is limited.
- Used for temporary works, boundary walls, retaining walls in hilly regions and terraces, where economy is important and drainage is needed.

```text
   ___  ____  ___
  |   \/    \/   |   stones interlocked,
  |__/\  __  /\__|   no mortar
  |  \ \/  \/ /  |
  |___\_/\__/\___|
```

| Point | Random rubble | Dry rubble |
|---|---|---|
| Mortar | Used | Not used |
| Strength | Higher | Lower |
| Water drainage | Poor | Free |
| Use | Foundations, walls | Retaining walls, boundary walls |

## Check yourself

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

1. What is characteristic of random rubble masonry?
   A. Stones laid with no mortar
   B. Irregular quarry stones laid in mortar without definite courses
   C. Bricks in header bond
   D. Dressed stones in regular courses
   Answer: B. Random rubble uses rough irregular stones with mortar filling the gaps. (Key point: Random rubble)

2. Why are through (bond) stones placed at about 1.5 m spacing?
   A. To drain water
   B. To bond the wall across its thickness
   C. To increase wall height
   D. To decorate
   Answer: B. Through stones tie the faces of the wall together. (Key point: Bond stones)

3. What makes a dry rubble wall stable?
   A. Cement mortar
   B. Interlocking and weight of stones, with chinking
   C. Steel reinforcement
   D. Lime plaster
   Answer: B. No mortar is used; fitted stones and small wedging stones give stability. (Key point: Dry rubble)

4. Why is dry rubble suited to retaining walls in hills?
   A. It is stronger than random rubble
   B. It drains water freely and is economical
   C. It needs thin walls
   D. It is waterproof
   Answer: B. Absence of mortar allows free drainage, and it is cheap. (Key point: Dry rubble use)

## Related in Building Technology

- [Rubble, coursed rubble and ashlar masonry](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Arubble-coursed-ashlar) — Building Technology, chapter 3, asked 2×