What Is Rubble Masonry?
Rubble Masonry is a type of stone masonry in which stones are used as obtained from the quarry or roughly dressed with wider joints in contrast to ashlar masonry wherein stones are given a fine finish and joints are also kept thin.
Rubble Masonry is the most commonly used stonework in most cases because of its ease in handling and cost-effectivity. Before the introduction to brick masonry, Rubble Masonry is widely used in the ancient world.
Why Rubble Masonry is Preferred?
- There is difficulty in dressing most type of stones. (this is the primary reason why rubble is preferred over ashlar)
- For economical construction (ashlar masonry is quite costly)
Strength of Rubble Masonry Depends on
- Physical characteristics of the stone.
- Quality of mortar used.
- Usage of long trough stones.
- Proper mortar filling in the voids after placing of stones; especially in joints.
- Climatic conditions
Rubble Masonry is Employed When,
- The surface is hidden.
- The backing of the wall while facing is employed Ashlar masonry.
- Aesthetics of the structure does not matter.
The Downside of Using Rubble Masonry as Hearting:
- It does not contribute to the wall’s strength.
- It is not aesthetically enticing as the undressed stones in the facing makes the building look unpleasant.
The use of stone masonry was practiced in earlier times as natural stone is available in our country in abundance. Many temples made out of stone still exist at various places around the country like Ellora caves.
Its usage can be detected in the medieval cathedral walls and some historic buildings. The cathedral walls have an outer facing of ashlar while inner hearting comprises dry rubble masonry.
Romans even used masonry in defensive walls during the medieval period. Its best example Colosseum in Rome, Italy. But, even during that period, brick construction enjoyed a preference.
Type of Rubble Masonry
The following are the most popular rubble masonry types used in construction,
- Uncoursed rubble masonry
- Coursed rubble masonry
- Built to regular courses
- Polygon rubble masonry
- Flint rubble masonry
- Dry rubble masonry
1. Uncoursed Rubble Masonry
In this type of masonry, stones are not arranged in a course, i.e. the stones are not placed in a horizontal layer rather just stacked over one another. That’s why it is called uncoursed rubble masonry.
Stones are utilized as obtained from the quarry, thus, making it the cheapest masonry construction as it saves the cost of dressing the stones.
But, as the stones are undressed, they vary in shape and size to a large extent. This results in poor bonding between the stones. This makes it the weakest masonry in terms of strength. Large stones are laid first followed by the filling of smaller stones in the voids.
Although the stones are used directly from the quarry without dressing, their projecting inconvenient corners are knocked off so that the bushing is
- Not more than 40 mm – for exposed walls without plaster
- Not more than 10 mm – for walls to be plastered
i) Uncoursed Random Rubble Masonry
The stone blocks are selected by a mason at random and placed roughly in a course so that a good bonding is achieved. Bigger stone blocks are laid at quoins & jambs to increase its strength. The weak corners and edges are removed with the help of a scabbling or spalling hammer.
As stones are used directly from the quarry, this masonry has varying appearances. The mason handpicks the blocks and places them to achieve a natural aesthetic appeal.
The minimum thickness that can be constructed with great care in ordinary buildings is 225 mm (9”). And if the construction is to be done with ease, 300 mm minimum thickness can be achieved.
- In-wall construction in ordinary buildings of low height.
ii) Uncoursed Square Rubble Masonry
The faces of the stones are given a straight finish with the help of a hammer.
The stones are laid along their natural beds, but in a random way without forming a course.
The voids are filled with mortar and stone chips. Care should be taken that chips are not laid on the bedding. Larger stones are placed at quoins.
Read More: What Is Pointing And 8 Types Of Pointing
2. Coursed Rubble Masonry
In this type of masonry, stones are arranged in a course, i.e. the stones are placed in a horizontal layer. That’s why it is called coursed rubble masonry.
i) Coursed Random Rubble Masonry
This type of masonry has hammer-dressed stones placed in a level course. The height of the stones should be more than their breadth, while its size varies between 5-10 cm.
The stones are laid in layers of equal height. If the smaller stones are encountered, then two or three stones are stacked one above another to obtain the height of the course in which it is placed. Such stones are placed in the intermediate courses and avoided at corners, bedding, and other critical locations.
To ensure sufficient strength of the masonry, 14th of the face stones are tailed into the work for a length of at least twice their height. And all the remaining ones should be tailed into for the length of their height.
In addition to this, for stability, a header course is introduced at regular intervals.
This masonry is suitable in hilly areas where stones are available in abundance at a cheaper rate. It is used in the construction of
- Low height walls of public buildings, residential buildings, etc.
- Boundary walls.
ii) Coursed Square Rubble Masonry
It is a superior variety of rubble masonry.
In this type of masonry, stones are chisel-dressed into an almost square shape and arranged in courses. These chisel-dressed square stone pieces are arranged in the facing while the backing constitutes of uncoursed random rubble masonry.
Though the height of the courses may vary, the height of stones in each course is almost kept equal. The height of the course is kept between 100-300 mm. The construction of backing and facing shall be done simultaneously.
The component – joint is the most crucial one in any construction. In this masonry, joints are to be kept uniform. Also, small chips of stones are used to avoid thick mortar joints.
A rockface appearance is attained by pitching the face of the stones. Or it can be dressed to give a smooth finish. Or smaller stones can be introduced in the same course, at intervals to produce a chequered effect.
I.S.: 1957 further classifies Coursed square rubble masonry into two types:
- First sort: Stones are squared on all joints. Bed joints are chisel dressed up to 80 mm into the face. Height of the courses should be minimum 150 mm. Also, the courses should be regular.
- Second sort: All requirements are the same as the first sort except that gap between joints should not be more than 10 mm and usage of chips should not exceed 15% of the total quantity of stones.
This masonry is extensively utilized in hilly areas where good quality stones are easily available for the construction of,
- Public buildings
3. Built to Regular Coursed Masonry
I.S. code refers to this type of masonry as Brought to course. In this type of masonry, stones of uniform height are laid in horizontal layers not less than 130 mm in height.
The stone beds are hammer/chisel dressed to at least 10 cm depth from the face to facilitate proper bonding. The vertical joints in the consecutive courses should not be allowed to coincide.
The construction pattern of this type of wall resembles that of uncoursed random rubble masonry. The major difference is that this masonry is roughly levelled up to courses at irregular intervals unlike the uncoursed random rubble masonry, where the stone pieces are not laid in courses.
The intervals in this masonry are decided on the basis of locality and the type of stones used. This interval is generally in-between 300-900 mm.
4. Polygon Rubble Masonry
In this type of masonry, the stones are roughly hammer-pitched into irregular polygonal shapes. The stones used here are mostly without prominent stratification.
These stones are embedded in the facing to show the irregularity of face joints in all directions for aesthetic appeal.
It is mostly similar to Course Rubble Masonry of the first sort.
Arrangement of Stones
- Long joints in facing are avoided.
- Joints are broken as much as possible so that they do not coincide vertically.
(Strength of the masonry is reduced to a great extent when joints of the adjacent courses are placed one above another). Small pieces of stones should be avoided in providing support to facing stones.
5. Flint Rubble Masonry
This type of masonry is generally put to use where flint/cobble is available in abundance. These stones are 8-15 cm thick, 15-30 cm long.
These stones are hard but brittle. They are laid in the facing, either coursed or uncoursed.
The brittleness of these stones reduces the strength of this masonry, which is supplemented by placing a Lacing course of thin stones/bricks at 1-2 m intervals in the vertical direction.
6. Dry Rubble Masonry
It is constructed in the form of random rubble masonry without mortar as its name suggests.
This is achieved by filling up the hollow spaces around the stones placed by smaller stone pieces and so on until the stones are tightly packed.
This is cheaper as the cost of mortar is nullified. But, at the same time, skilled manpower is required to manage the stones alone without mortar.
The height of the stone pieces should be,
- In no case greater than 6 m
- If it is greater than 3 m, three adjacent courses are laid & at 3 m intervals in square rubble masonry.
- Non-load bearing walls- retaining walls
- Pitching of earthen dams & canal slopes
Different Types of Stone Rubble Masonry and Their Applications
|1. Uncoursed rubble random||No dressing; Directly from QUARRY||Laid randomly||In-wall construction of low heights|
|i) Uncoursed Square Rubble||straight finish||Randomly, but on
|In hilly areas, where
these stones are available in abundance
|2. Coursed Random Rubble||Hammer dressed||Placed in a levelled
|Low height walls of public buildings, residential
buildings, etc, Boundary walls
|i) Coursed Square Rubble||Chisel-dressed into an
almost square shape
|Carefully arranged in
|Construction of Public
buildings, Hospital, Schools
|3. Built to regular course||Hammer/chisel dressed
to at least 10 cm depth from the face
|Roughly levelled up to
courses at irregular
|4. Polygonal rubble masonry||roughly hammer-pitched
into an irregular polygonal shape
|Laid in course; similar to coursed rubble masonry||Walls of forts, as in
Great Wall of India(Rajasthan)Walls
|5. Flint rubble masonry||Chiselled & carved in such
a way to improve aesthetics
of the building
|Laid in the facing, either coursed or uncoursed||Construction of churches, houses, etc.Townhall walls|
|6. Dry rubble masonry||Either used directly or
chisel dressed into the desired shape depending upon the aesthetic required
|Laid randomly; similar
to Uncoursed random rubble masonry WITHOUT mortar
walls- retaining walls, Compound walls,
Pitching of earthen dams & canal slopes
Watch Video: Construction of Stone Rubble Masonry
You May Also Like: