Table of Contents
The art of construction of stone units bonded together with mortar is called stone masonry.
✔ Stone masonry is used in building foundations, retaining walls, arches, floors, walls & columns.
✔ Mostly natural rocks are used in stone masonry. Natural rocks are cut and dressed into proper shape before use.
✔ Stone masonry is very strong & durable. The strength mainly depends upon the types of stones or the mortar used.
1. Materials Used in Stone Masonry
Materials used in stone masonry are:
Stones to be used in stone masonry should be hard, durable, tough, and free from cavities, sand holes, and cracks.
The selection of stones should be done based on the availability of stones and the importance of structure.
Limestone, sandstone, granite, marble, laterite, etc are the commonly used stones in masonry.
Cement and lime mortar are commonly used in this masonry.
The selection of mortar depends upon the strength required, the color of the stone, and loads coming from the structure.
2. General Principle in Stone Masonry
The following point should be considered while supervising the stone masonry.
~ The stone used should be strong, tough, hard, and free from cracks and cavities.
~ Each stone should be well-wetted before use so that it does not absorb water from mortar.
~ The stone should be dressed properly according to the types of masonry.
~ Masonry works should be raised uniformly.
~ Broken stones should not be used for facing and backing.
~ Wall should be laid completely vertical.
~ If stone masonry is to be carried out at a higher level, double scaffolding should be used.
~ No tensile stress should be produced anywhere because the stone is weak in tensile strength.
3. Tools used in Stone Masonry
Some common tools used in stone masonry are:
a. Spalling Hammer
d. Iron Hammer
f. Claw Tool
j. Pitching Tool
4. Recommendations For Type of Stone
|S.No||Purpose||Type of Stone to be used|
|1.||Heavy Engineering works such as ducks, breakwaters, bridges, piers, etc. carry a high intensity of pressure.||Fine-grained granite and gneisses.|
|2.||Masonry work in an industrial area, exposed to smoke and chemical fumes.||Granite, compact sandstone, and quartzite.|
|3.||General Building work||Limestone and sandstone|
|4.||Facework of building||Marble, granite, and closed-grained sandstone.|
|5.||Carvings and ornamental work||Marble, laterite, and soft sandstone.|
|6.||Pavings, door sills, steps||Slate, sandstone, marble|
|7.||Fire-resistant masonry||Compact stone.|
5. Types of Stone Masonry
1) Rubble masonry
✔ In this masonry, undressed or roughly dressed stones are utilized.
✔ This masonry has wide joints since stones of irregular sizes are used.
✔ Rubble masonry may be out of the following types:
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 this 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.
2) Ashlar Masonry
The stone masonry constructed using finely dressed stone blocks is called ashlar masonry.
✔ The stone blocks may be either square or rectangular shaped.
✔ The height of stone varies from 25 to 30 cm.
Some features of ashlar masonry are:
a. The courses are of uniform height.
b. All the joints of this masonry are regular, thin, and have a uniform thickness.
c. Ashlar masonry is mostly used in the construction of heavy structures, architectural buildings, high piers, and abutments of bridges.
✔ The height of blocks in each is kept equal but it is not necessary to keep all the courses of the same height. Ashlar masonry may be divided into the following categories:
a. Ashlar Fine Tooled
This is the finest type of stone masonry work.
Each stone is cut to the regular and required size and shape so as to have all sides rectangular so that the stone gives perfectly horizontal and vertical joints with adjoining stones.
The beds, joints, and faces are chisel-dressed, such that all waviness and unevenness are completely removed and a fairly smooth surface is obtained.
The face which remains exposed in the final work is so dressed that no point on the dressed face is more than 1 mm from a 600 mm long straight edge placed on the surface in any direction.
The top and bed are also so dressed that no point on the surface is more than 3 mm, from the straight edge.
The side surfaces to form the vertical joints are also depressed that no point on the surface is more than 6 mm from the straight edge.
The surfaces forming internal joints which are not visible are also so dressed that at no point in the surface is more than 10 mm from the straight edge.
All the angles and edges that remain exposed in the final position are kept as true square and free from chipplings. The thickness of courses is generally less than 15 cm. The width of the stone is not kept less than its height.
Headers and stretchers are laid alternatively in each course or courses of headers and courses of stretchers may be laid alternatively or they may be laid as otherwise directed.
The thickness of the mortar joint is finely pointed.
b. Ashlar Rough Tooled Masonry (Bastard Ashlar)
In this type of masonry, the beds and sides of each stone block are finely chisels dressed just in the same manner as for ashlar fine, but the exposed face is dressed by rough tooling.
A strip, about 25 mm wide and made by means of a chisel is provided around the perimeter of the roughly dressed faces of each stone.
The rough tooled face when tested with a straight edge 600 mm in length, should not show any point on the surface to vary by more than3 mm in any direction.
This type of masonry is also known as bastard masonry.
The size, angles, edges, etc are maintained in order, similar to that for fine-dressed ashlar.
The thickness of the mortar joint should not be more than 6 mm.
|Read Also: Quarrying of stone|
c. Ashlar Rock or Quarry Faced
In this type of masonry, the exp[osed surface face of the stone is not dressed but is kept as such so as to give rock facing. However, a strip of about 25 mm wide, made by means of a chisel, is provided around the perimeter of the exposed face of every stone.
The projections on the exposed face (Known as bushings) exceeding 80 mm in height are removed by light hammering. Each stone block, however, is maintained true to its size, with perfectly straight side faces and beds, and truly rectangular in shape.
This type of construction gives a massive appearance. The height of each block may vary from 15 cm to 30 cm. The thickness of the mortar joint may be up to 10 mm.
d. Ashlar Chamfered Masonry
This is a special form of rock-faced ashlar masonry in which the strip provided around the perimeter of the exposed face is chamfered or beveled at an angle of 45º by means of a chisel to a depth of 25 mm. Due to this, a groove is formed in between adjacent blocks of stone.
Around this beveled strip, another strip of 15 cm is dressed with the help of a chisel. The space inside this strip is kept rock-faced except that large bushings in excess of 80 mm projections are removed by a hammer.
e. Ashlar Block in Course Masonry
This type of masonry is intermediate between rubble masonry and ashlar masonry.
The faces of each stone are hammer-dressed, and the height of blocks is kept the same in any course though it is not necessary to keep the uniform height for all the courses.
The vertical joints are not as straight and as fine as in ashlar masonry.
The depth of courses may vary from 15 to 30 cm.
This type of masonry is adopted in heavy works such as:
✔ Retaining walls
f. Ashlar Facing
Ashlar facing masonry is provided along with brick or concrete block masonry, to give a better appearance.
The sides and beds of each block are properly dressed so as to make them true to shape.
The exposed faces of the stones are tough tooled and chamfered. The backing of the wall may be made in brick masonry.
|Read Also: Artificial Stones|
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