Stone masonry

STONE MASONRY

Stone is a natural choice for masonry, if available in plenty. Its durability has been demonstrated in our temples and massive structures. Coal tar, Paraffin, Linseed oil or Solution of alum and soap are the Preservatives used to prevent the stone from the effects of rain water, wind, etc.

Stone Masonry is the construction carried out using stones with mortar. Due to high cost of transportation, costly work of dressing and the need for experienced labour, stone masonry is not popular. Further, stone masonry walls occupy more space compared to brick masonry walls.

Types of Stones: Types of stones used in stone masonry are:

1. Dense stones like Granites and Quartzite

2. Fire-resistant stones, namely, Sandstones

3. Soft stones like Lime Stones, Marbles and Slates used for carvings, arches, etc.

Uses of Stone Masonry

• Foundation, floor, walls, lintels, columns, roofs, etc.

• Walls, roofs, lintels for temples, monuments, etc.

• For facing works in brick masonry to give a massive appearance.

 

1. DRESSING OF STONES

After quarrying, stones are to be dressed for surface finish. Dressing of Stone is the art of cutting the stones to the shape required for use in structures. It is done at the quarry itself. The Quarry Dressing has the following advantages in comparison to Site Dressing:

• Cheap labour is available at the quarry site.

• Freshly quarried stones contain some moisture called Quarry Sap. Hence, they are comparatively soft and can be easily dressed.

• It is possible to sort out the stones at the quarry for different works. Irregular and rough portions of the stones can be removed then and there in the quarry. Thus, the weights of the stones as well as the transportation of stones are reduced.

Tools Used for Dressing of Stones: Hammers, Chisels, Axes, Punching Machine, etc.

1. Types of Dressing

1. Hammer Dressing: For Rubble Masonry, stones are roughly dressed with hammers. The surface thus obtained is called Hammer-Dressed. The stones are made roughly square or rectangular or polygonal. Lower and upper surfaces of stones are almost dressed flat.

2. Chisel Dressing: For good Ashlar Masonry, the faces of stones are finely dressed by chisels. Its front face is dressed to rock face.

3. Axed Finish: Axe is used for the dressing operation. Axed Finish is employed in hard stones like Granites.

4. Polished Finish: Granite and Marble take a good polish. This is achieved manually or by the aid of polishing machines.

 

2. TERMINOLOGY OF STONE MASONRY [Figs. 1(i), (ii), (iii) and (iv)]

1. Natural Bed: The surface on which the materials were originally deposited in the formation of rock is known as Natural Bed.

2. Plinth: Plinth is the projecting course at the Ground Floor Level. It is used to indicate the height of Ground Floor Level from Ground Level. The plinth course protects the interior of a building from rain water, frost, etc.

3. Corbel: Corbel is a stone piece provided in a wall. It projects partly outside, which acts as bearing for the structural member such as beam, roof truss, etc., resting on it.

4. Cornice: It is placed at the top of a wall or ceiling near the top of the building.

5. Coping: Coping is a course of stone or brick placed on the top of a Parapet wall. It protects the wall from seepage of rain water through joints at the topmost course of the wall.

6. Throating: Throating is a small groove cut on the underside of Coping, Cornice and Sunshade. It is provided to discharge rain water without trickling down to the walls.

7. Weathering: Weathering is a slope provided to the top surface of stones used for coping and cornice to drain-off the water immediately.

8. Through Stones or Bond Stones: In stone masonry, some long stones at regular intervals are placed through the full thickness of a wall to develop bond. Such stones are known as Through Stones or Bond Stones.

9. Jamb: Jamb is the vertical side of the opening of masonry for door, window, etc. It may be plain or is provided with the recess to receive the frames of door and window.

10. Hearting: Hearting is a filled-up core of a rubble wall.

11. Lintels or Heads: Lintels are the horizontal stones provided at the top of the openings for doors, windows, etc.

 

3.  CLASSIFICATION OF STONE MASONRY

Stone Masonry is classified based on (i) Thickness of joints, (ii) Continuity of courses and (iii) Finish of face. The two broad classifications of stone masonry are:

1. RUBBLE MASONRY

(i) Random Rubble Masonry

Un-coursed and Coursed

(ii) Squared Rubble Masonry

Un-coursed and Coursed

(iii) Polygonal Rubble Masonry

2. ASHLAR MASONRY

(i) Ashlar Fine Masonry

(ii) Ashlar Rough-Tooled Masonry

(iii) Ashlar Rock or Quarry Faced Masonry

(iv) Ashlar Chamfered Masonry

(v) Ashlar Facing Masonry

1. RUBBLE MASONRY

A Rubble Stone Masonry wall is made up of stones of irregular sizes and shapes. The stones from the quarry are broken into small sizes. These are directly used in the construction work. In some cases, these stones may be shaped to suit the requirement, with the help of hammers. These stones have rounded natural faces or angular broken pieces.

Rubble Masonry is further classified into three types. They are explained below.

(i) Random Rubble Masonry

Random Rubble Masonry uses stones of irregular shapes. The stones are arranged in a random fashion. The joints are pointed to achieve a good appearance. Random Rubble Masonry may be either Un-coursed or Coursed as explained below:

a) Un-coursed Random Rubble Masonry

See Fig. 2. It is the cheapest type of stone masonry. Stone blocks are not dressed, but used as obtained from the quarry. They are of varying sizes and placed in irregular pattern.

Vertical joints are not constructed in plumb. So, no regular courses are achieved.

Spaces between larger stones are filled with Spalls (small stones of irregular sizes) and packed in mortar. The appearance is not very pleasing.

Uses. It is used for compound walls, godowns and walls of unimportant structures.

b) Coursed Random Rubble Masonry

See Fig. 3. In this, stones are hammer-dressed. Stones of equal height are used in every course of the stone masonry. Thus, masonry work is carried out in courses. Through Stones are used at every 2 meter distance in each course to form bond.

Uses: It is used for residential buildings, industrial buildings, compound walls, warehouses, etc.

(ii) Square Rubble Masonry

In this type, the stones are roughly squared with straight edges and sides with hammer blows.

a) Un-coursed Square Rubble Masonry (Fig. 4)

In this type, the stones are of varying sizes of different heights, but with straight edges and sides. They are laid in irregular pattern. Hence, no regular courses are achieved.

Good appearance is achieved by using Risers, Levellers and Snecks in a pattern as shown. Snecks are used to prevent the occurrence of long continuous joints.

b) Coursed Square Rubble Masonry (Fig. 5)

This type of masonry also uses the same stones as used for un-coursed square rubble. But, the work is carried out and levelled in courses of different heights.

Each course consists of Headers, Levellers and Through Stones of the same height as shown.

(iii) Polygonal Rubble Masonry

In this, the stones are hammer finished on the face of the wall to an irregular polygonal shape.

2. ASHLAR MASONRY

In Ashlar Masonry, no irregular stones are used. The entire construction is done using square or rectangular dressed stone blocks. The beds, sides and faces of the stones used in this masonry are all dressed finely with chisel. This masonry is laid in courses with thin end joints. It is the highest grade of masonry and costly. By arranging stones in various patterns, different types of appearances can be obtained. Types of ashlar masonry are explained below:

(i) Ashlar Fine Masonry (Fig. 6)

In this masonry, each stone is cut to uniform size and shape with rectangular sides. Therefore, it gives perfect horizontal and vertical joints with a smooth appearance.

The face stones are laid as Headers (H) and Stretchers (S) alternatively. For walls having thickness less than 75 cm, Through Stones should be used at suitable intervals at each course for proper bond.

(ii) Ashlar Rough-Tooled Masonry

In this type, the beds and sides of each stone block are finely chisel-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 is provided around the perimeter of the rough dressed face of each stone.

(iii) Ashlar Rock or Quarry Faced Masonry

In this type, a strip of 25 mm wide is provided around the perimeter of the exposed face of each stone as in the case of rough-tooled masonry. However, the remaining portion of the face of the stone is left in the same form as received from the quarry. It is not dressed. It is kept as such so as to give rock or quarry facing. Each stone block is maintained to its size with perfect straight sides, faces and beds and truly rectangular in shape.

(iv) Ashlar Chamfered Masonry (Fig. 7)

It is a special form of Rock-faced Ahslar Masonry.

In this type, a strip provided around the perimeter of the exposed face is chamfered at 45o. Due to this, a Groove is formed in between the adjacent blocks of stone.

Around this chamfered strip, another strip of 10 mm to 12 mm wide is dressed. The space inside this strip is kept rock-faced, except the large projections that are removed by a hammer.

(v) Ashlar Facing Masonry (Fig. 8)

This masonry is a combination of Ahslar Masonry and Rubble Masonry.

In this type, only face work is provided with rough tooled or hammer dressed stones. Backing of the wall may be made in rubble masonry or brick masonry or concrete.

The beds and sides except exposed face are dressed perfectly fine and square.

Uses: This masonry is used for retaining walls, sea walls, etc.

(vi) Ashlar Block-in-Course Masonry

This type is an intermediate approach between the ashlar masonry and rubble masonry. It is constructed of large stone blocks. The faces of each stone block are hammer dressed. It is a coursed rubble masonry of superior variety.

 

4. PRINCIPLES OF STONE MASONRY CONSTRUCTION

[Precautions to be observed in Stone Masonry]

1. Quality: Stones of stone masonry should be hard, strong, tough and durable.

2. Dressing: Proper dressing of stones have to be done according to the type of masonry.

3. Natural Bed: All the stones should be laid on the natural bed only.

4. Mortar: Cement mortar or sometimes rich lime mortar in suitable proportion is used.

5. Pressure Acting on the Stone: Stones in the stone masonry are lied such that the pressure acting on the stones is perpendicular to the natural bed of the stones.

6. Tensile Load: Stone masonry work should not be designed to take any tensile load.

7. Watering: Stones should be watered well before use to prevent water absorption from mortar.

8. Courses of Stones: Different courses of stones should be laid perpendicular to the line of action of pressure on the stones.

9. Through Stones: Through Stones should be used sufficiently such that they cover about 15 to 25% of the area in elevation. This is to ensure proper bonding.

10. Vertical Joints: Vertical joints should be staggered. Extreme care has to be taken by providing proper bond to prevent formation of vertical joints.

11. Surface of Stone Masonry: Surfaces of stone masonry should always be kept wet, while the work is in progress and also till the mortar has set.

12. Facing of Stone Masonry: Small stone pieces are used for facing of stone masonry.

13. Hearting: Hearting of masonry should be properly packed with stone chips and mortar.

14. Verticality: Verticality of faces of stone masonry walls are checked with a Plumb Rule.

15. Inclined Surfaces: Inclined surfaces should be checked with Wooden Templates.

16. Unequal Settlement: Stone wall should be raised uniformly throughout its length. It will avoid possible unequal settlement.

17. Voids in Masonry: Voids in stone masonry should not be dry-packed or filled with small size aggregates. Instead, they should be well-packed with large aggregates and mortar.

18. Stepped Raking: Unfinished end of stone masonry should be raked back. This stepped raking develops proper bond between the old and the new works.

19. Curing: After the construction is over, the whole masonry work should be kept cured for 2-3 weeks, if laid in lime mortar and for 1-2 weeks if cement mortar is used.

 

5.  COMPARISON OF BRICK MASONRY AND STONE MASONRY