Following are the general principles and precautions in stone masonry
1. The stones to be used for masonry should be hard, durable and tough. All stones should be free from defects and decays.
2. Through or bond stones should be selected separately from ordinary building stones.
3. All stones for masonry in cement or lime mortar must be thoroughly wetted before being laid down so that they may not absorb moisture from mortar and thereby reduce its strength.
4. The stones should be properly dressed before placing them in position.
5. The stones should be placed in a structure on their natural quarry bed so that the pressure to be taken by them is normal to the beds.
6. The prescribed number of through or bond stones must be used in order to provide sufficient lateral stability to the structure.
7. The stones must be laid in such way that they should break the continuity of vertical joints in the structure.
8. Quoins should be laid as header and stretcher in alternate courses.
9. In case of vertical wall, the face of the wall should be exactly verticality and good stones template. should be used for face-work. Verticality of the face may be checked with a
10. All lintels and inside stones, not to be plastered over, should be of the full thickness of the wall, including the thickness of the plastered faces.
11. The joints on surface should be raked atleast 25mm deep and pointed with rich cement motar.
12. The masonry in entire length of the wall must be uniformly raised. Proper toothing must be provided to bind it to the wall to be built afterwards.
13. All iron, stone, concrete or other fixtures, buttresses etc. should be built and bonded into the masonry in the correct position as the work proceeds.
14. Stone masonry laid in cement or lime mortar should be protected during construction from the effects of rains and frosts by a suitable cover.
15. The hearting of the masonry should be properly packed with mortar and stone chips i.e. spalls, to avoid any hollows or very thick mortar joints.
Important technical terms related to stone masonry?
Following are the important technical terms related to stone masonry:
1. Natural bed of stone: The original surface occupied by a stone during its formation is called the natural bed of stones. The building stones are derived from rocks. These rocks have a distinct plane of division along which the stones can easily be splitted. Such a plane represents the natural bed of stones.
2. Bedding plane: The plane along which the stone can be separated into different layers is called bedding plane. In stone masonry each stone should be placed in such a manner that the pressure acts at right angles to the plane of the bedding so that it can take more load.
3. String course: A horizontal course of masonry provided at roof floor level projecting outside of the building is known as string course. The purpose of providing string course is to throw out the rainwater which may otherwise slide along the wall of the surface and may cause dampness in the building.
4 Corbet: A piece of stone projecting from wall to the provide support to any structural member of the roof or floor is called corbel, and the process of providing corbel is called corbelling.
5. Cornice: A large moulded course of masonry provided at ceiling level of the roof which projects outside the surface of the wall of the building is called cornice. The purpose of providing cornice for achieving architectural appearance and also to throw the rain water away from the surface of the exposed wall.
6. Block-in-course: The course of stone provided on the top of the cornice to hold down and to prevent the cornice from overturning is know as block in course or blocking course.
Type of stone masonry/Rubble masonry/Ashlar masonry/Its aplication
Following are the specifications for coursed rubble masonry
1. All the stones shall be laid in horizontal courses not less than 150mm height.
2. All the stones in each course shall be of equal height and all courses shall be of the same height unless otherwise specified.
3. All stones shall be set full in mortar in all bed or vertical joints. All beds shall be horizontal and joints vertical.
4. The face stone shall be squared on all joints and beds by hammer dressing with the help of masonry hammer. No face stone shall be less in breadth than its height.
5. The quoins shall be of the same height as the course in which they occur.
6. Through stones shall be inserted at the rate of one per square metre of the area
7. The work on the internal face shall be same as on the exterior face unless the work is to be plastered.
8. All the stones should be wetted before laying.
9. The whole masonry shall be carried up at a uniform level throughout.
10. Mortar shall be confined to the joints and shall not come over the faces of stones which are not to be plastered.
Following are the specifications of the ashlar masonry
1. Ashlar masonry shall be laid in the specified mortar and in regular courses not less than 300mm or 0.3m in height.
2. All the courses shall be of the same height unless otherwise specified.
3. All the joints and beds shall be perfectly vertical and horizontal respectively. All stones shall be set full in mortar in all beds and vertical joints.
4. All the stones shall be wetted before laying.
5. The face stone shall be laid in Flemish bond with headers and stretchers alternatively in the same course, unless otherwise specified.
6. To obtain sufficient transverse bond, the prescribed number of through or bond stones shall be used.
7. Mortar shall be confined to the joints and shall not come over the faces of stones which are not to beplastered.
8. Masonry laid in cement or lime mortar shall be protected during construction from the effects of rain and frost by suitable cover, if necessary.
9. Bed plates shall be provided under the ends of beams, girders, roof trusses, etc.
10. In case of the vertical walls, all the masonry shall be taken up truly plumb.
Different types of ashlar masonry?
The different types of Ashlar masonry are:
a) Ashlar fine or coursed ashlar masonry: In this type of masonry stone blocks of same height in each course are used. Every stone is fine tooled on all sides. Thickness of mortar joints is uniform throughout. It is expensive type of stone masonry as it involves heavy labour and wastage of material while dressing the stones.
b) Random course ashlar masonry: This type of ashlar masonry consists of fine coursed ashlar but the courses are of varying thickness depending upon the character of buildings.
c) Rough tooled or bastard ashlar masonry: In this type of ashlar masonry, the sides of the stones are rough tooled and dressed with chisels. Thickness of the joints is uniform, which does not exceed 6mm.
d) Rock or quarry-faced ashlar masonry: This type of ashlar masonry is similar to rough tooled type except that there is chisel drafted margin left rough on the face, which is known as quarry faced.
e) Chamfered ashlar masonry: It is similar to quarry faced ashlar masonry except that the edges are bevelled or chamfered to 45° for depth of 25mm or more.
f) Block-in-course masonry: It is the name given to a class of ashlar masonry which occupies an intermediate place between the rubble and ashlar masonry. The stones are all squared and properly dressed. It resembles to coursed rubble and rough tooled ashlar masonry.
g) Ashlar facing: Ashlar is the best type of stone masonry. Since this is very expensive, it is not commonly used throughout the whole thickness of the wall, except in works of great importance and strength.
In order to reduce the cost and give appearance of ashlar facing to the wall it is usual practice to construct the walls with the facing of ashlar and backing of rubble or brick masonry.
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