Stone Masonry

Stones are abundantly available in nature which can be properly shaped and used for construction of various parts of a building. Similar to brick masonry, stones also can be systematically arranged to form a homogeneous mass called stone masonry. The materials used for stone masonry are stones and mortar. The common types of stones used for stone masonry in India are: granites, sandstones, limestones, marbles and slates. Stone masonry is strong and durable.

Apart from the use in building construction, stones are used for structures like dams, piers, waterfront works, monuments and memorials. Stone masonry is not affected by dampness and does not require plastering. However, it will be cheap only in areas where it is abundantly available.

Terminology

1. Bed Surface

Surface of a stone perpendicular to the line of pressure.

2. String Course

A horizontal course of masonry continuously projecting from the face of the wall.

3. Corbel

A stone embedded in a wall to support a structural member.

4. Cornice

A moulded projection of masonry on the top of a wall.

5. Through Stone

Stone extending throughout the thickness of the wall.

6. Hearting

A filled-up core of a rubble wall.

7. Jam

A masonry portion forming the side of an opening.

16.3.2 Materials Used

Materials used for stone masonry are stones and mortar. Common types of stones which are used for stone masonry along with their crushing strength are presented in Table 16.3.

Table 16.3 Common types of stones used for stone necessary

Generally lime and cement mortars are used for stone masonry. Their function is to initially provide a workable matrix and ultimately a hard-binding material, which renders masonry into a monolithic unit. Hydraulic lime and Portland cement with river sand are used.

16.3.3 Cutting and Dressing of Stones

Dressing is the art of cutting the stones to shape required for use in structures. A brief discussion on dressing and purpose of dressing is made in Section 2.8.

Tools used for cutting and dressing stones is given in Fig. 16.5.

Figure 16.5 Tools for cutting and dressing stones

Stones for two major types of stone masonry, viz., rubble and ashlar masonry (discussed in Section 16.3.4) are dressed as follows.

1. Dressing for Rubble Masonry

1. For this type of masonry, stones are shaped by means of hammer. Lower and upper surfaces of stones are almost dressed flat.
2. For this type of masonry, stones which have front face almost rectangular and remaining irregular are also used.

2. Dressing for Ashlar Masonry

1. For this type of masonry, the faces of stones are finely dressed by means of chisels.
2. Further, chiselled faces are sometimes rubbed to give a smooth surface in case of special works like monumental works.

Different types of surface finishes adopted are presented in Fig. 16.6.

1. Rough tooled surface
2. Tooled surface
3. Cut stone surface
4. Hammer dressed surface
5. Polished surface
6. Rubbed surface

Figure 16.6 Types of surface finishes

16.3.4 Types of Stone Masonry

Stone masonry is classified based on the thickness of joints, continuity of courses and finish of face. Rubble Masonry and Ashlar Masonry are discussed below (IS: 1597, Parts 1 and 2, 1992).

1. Rubble Masonry

Rubble masonry is a stonework wherein blocks of stones are either undressed or roughly dressed and have wider joints. The stones used are not of uniform size and shape but generally of pyramidal in shape to some extent. Vertical and transverse bonds have to be attained. Through stones are provided from back to the face of wall to ensure better bonding. The strength of this masonry depends on the quality of mortar, use of through stones and filling of spaces. There are different types of rubble masonry, viz., random rubble, squared rubble and polygonal rubble. Figure 16.7 shows the various types of rubble masonry.

Figure 16.7 Types of rubble masonry

2. Ashlar Masonry

Ashlar masonry is a stonework wherein blocks of stones are accurately dressed with very fine joints of 3 mm thickness. It is essential to ensure that the sizes of individual stones are in conformity with the general properties of the wall. In this masonry the beds, sides and faces are finely chisel dressed. The backing of such walls may be rubble or ashlar masonry. It is the highest grade of masonry and costly. There are different types of ashlar masonry, viz., ashlar fine, ashlar rough tooled, ashlar rock or quarry faced, ashlar chamfered and ashlar facing. Figure 16.8 shows some of the types of ashlar masonry.

Figure 16.8 Types of ashlar masonry

3. Sub-divisions of Rubble and Ashlar Masonry

Various sub-divisions of these types are:

(i) Rubble Masonry

1. Random Rubble(i) Uncoursed(ii) Coursed
2. Square Rubble(i) Uncoursed(ii) Coursed(iii) Built to regular courses
3. Miscellaneous(i) Polygonal(ii) Flint

(ii) Ashlar Masonry

1. Ashlar fine
2. Ashlar rough tooled
3. Ashlar rock or quarry faced
4. Ashlar chamfered
5. Ashlar facing
6. Ashlar block-in-course

16.3.5 General Principles of Construction of Stone Masonry

The construction procedure for stone masonry is slightly different from that of brick masonry. Unlike in brick masonry, in stone masonry stones of different sizes and shapes are used and accordingly there is slight variation in construction. However, basically the requirements of vertical joints not being continuous, thickness of mortar joints and quality of mortar, verticality and perpendicularity of bonds, and the overall stability of wall are same in both. Even in stone masonry, procedures differ slightly between rubble and ashlar masonry constructions. However, the following general principles of construction should be observed while supervising the stony masonry construction:

1. Stones should be hard, tough and durable.
2. Pressure acting on the stone should be perpendicular to the bedding planes.
3. Stone masonry work should not be designed to take any tension.
4. Stones should be well watered before use.
5. Through stones should be used sufficiently such that they cover about 15–25% of the area in elevation.
6. Stones should be laid on its natural bed.
7. Extreme care has to be taken by providing proper bond to prevent formation of vertical joints.
8. Hearting of masonry should be properly packed with chips and mortar.
9. Verticality of the faces of the masonry walls should be checked with a plumb rule.
10. Portions of the masonry should be raised uniformly throughout its length.
11. Cement mortar and sometimes rich lime mortar may be used.
12. Proper dressing of stones has to be done wherever needed.
13. Surfaces of the stone masonry should be kept wet while the work is in progress and also till the mortar has set.
14. All laid fine dressed stonework should be protected against damage during further construction.

Comparison of Brick and Stone Masonry

Brick masonry and stone masonry are compared in Table 16.4.

Table 16.4 Comparison of brick and stone masonry