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The art of construction of stone units bonded together with mortar is called stone masonry. The stone masonry in which undressed or roughly dressed stones are utilized is called Rubble Masonry.
✔ This masonry has wide joints since stones of irregular sizes are used.
✔ Rubble masonry may be out of the following types:
Types of Rubble Masonry
a. Random Rubble Masonry
Masonry constructed using undressed or partially dressed stones in a random order is called Random Rubble Masonry.
There are 2- types of random rubble masonry:
1. Uncoursed Random Rubble Masonry
This is the roughest and cheapest form of stone-walling.
In this type of masonry, the stones used are of widely different sizes.
Since the stones are not of uniform size and shape; greater care and integrity have to be exercised in arranging them in such a way that they adequately distribute the pressure over the maximum area, and at the same time, long continuous vertical joints are avoided.
Sound bond should be available both transversely as well as longitudinally. A transverse bond is obtained by the liberal use of headers.
Larger stones are selected for quoins and jambs to give increased strength and a better appearance. This type of masonry is also known as uncoursed rubble masonry.
Some of the features of Uncoursed Random Rubble Masonry are:
a. It is the cheapest and roughest type of masonry.
b. It has a varying appearance.
c. Corners of stones are slightly knocked off before using.
d. To increase the strength of this masonry, large stones are used at corners and jambs.
e. “Through stone” is used in every square meter for joining faces and backing.
2. Built to Courses: Random Rubble Masonry
The method of construction is the same as above except that the work is roughly leveled up to form courses varying from 30 to 45 cm thick.
All the courses are not of the same height.
For the construction of this type of masonry, quoins are built first and a line (string) is stretched between the tops of quoins.
The intervening walling is then brought up to this level by using different sizes of stones.
The figure below shows the procedure, in which the stone has been numbered in the order in which they are placed. This form of masonry is better than uncoursed random rubble masonry.
b. Squared Rubble Masonry
The type of rubble masonry in which face stones are squared on all joints and beds by dressing before laying is called Square Rubble Masonry.
There are 3 types of square rubble masonry which are explained below:
a. UnCoursed Square Rubble Masonry
Square rubble masonry uses stones having straight beds and sides. The stones are usually squared and brought to a hammer-dressed or straight cut finish.
In the uncoursed square rubble, also sometimes known as square-snecked rubble, the stones with straight edges and sides are available in different sizes (heights). They are arranged on the face in several irregular patterns.
A good appearance can be achieved by using risers ( a large stone, usually a through stone), levelers (thinner stones), and sneck or check (small stone) in a pattern, having their depths in the ratio of 3: 2: 1 respectively.
Snecks are the characteristics of this type of construction, and hence the name. This prevents the occurrence of long continuous joints.
Note: L means Leveller. S means Sneck. R means Risers.
b. Square Rubble: Built to Courses
This type of masonry also uses the same stones as used for uncoursed square rubble. But the work is level up to courses of varying depth. The courses are of different heights.
Each course may consist of quoins, jamb stones, bonders, and thoughts of the same height with smaller stones built in between them up to the height of the larger stones, to complete the course.
Note: T means larger stones.
c. Square Rubble: Regular Coursed
In this type of masonry, the wall consists of various courses of varying heights, but the height of stones in one particular course is the same.
When the height of the courses is equal it is usually called coursed rubble masonry (CR masonry).
Some features of square rubble regular coursed masonry are:
a. It is a superior variety of rubble masonry.
b. Stones used are squared on all joints and beds and laid in courses.
c. Stones are laid in courses of equal layers.
d. Joints are uniform.
c. Miscellaneous Types
a. Polygonal Walling (Polygonal Rubble Masonry)
In this type, the stones are hammer finished on the face to an irregular polygonal shape. These stones are bedded in position to show face joints running irregularly in all directions.
Two types of polygonal walling may be there.
In the first type, the stones are only roughly shaped, resulting in the only rough fitting. Such work is known as rough picked work.
In the second type, the faces of stones are more carefully formed so that they fit more closely. Such work is known as close-picked work.
b. Flint Walling (Flint Rubble Masonry)
The stones used in this masonry are flints or cobbles, which vary in width and thickness from 7.5 to 15 cm and in length from 15 to 30 cm. These are irregularly shaped nodules of silica. The stones are extremely hard. But they are brittle and therefore may break easily.
The face arrangement of the cobbles may be either coursed or uncoursed or built to courses.
The strength of the flint wall may be increased by introducing lacing courses of either thin long stones or bricks at a vertical interval of 1 to 2 meters.
d. Dry Rubble Masonry
The rubble masonry constructed without using mortar or other binding agents is called Dry Rubble Masonry.
Un-dressed or partially dressed stones are used in this masonry.
It is suitable for constructing walls of a height less than 6 m.
Read Also: Artificial Stones
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