Stone Masonry Construction – Materials and Classification
Stone masonry is a type of building masonry construction that uses stones and mortar. This construction technique is used for building foundations, floors, retaining walls, arches, walls and columns. The stones used for masonry construction are natural rocks. These natural rocks are cut and dressed into proper shape in order to use it in masonry construction. Stones are one of the most durable and strong building materials.
The materials and the types of stone masonry construction are briefly explained.
Materials Used for Stone Masonry
The materials used for stone masonry are:
The stones used for masonry construction must be hard, tough and free from cracks, sand holes, and cavities. The selection of stone for particular work is dependent on the availability of the stone and the importance of the structure. The common stones used for masonry construction are limestone, sandstone, granite, marble, laterite, etc.
The binding material used for masonry construction is the mortar. Cement or lime with sand and water form the mix for masonry mortar. The mix formed is uniform in nature. The two main factors affecting the selection of mortar for masonry are:
- Strength required
- Colour of the stone
- The loads coming on the structure
Classification of Stone Masonry
The two main classifications of Stone Masonry are:
- Rubble Masonry
- Ashlar Masonry
1. Rubble Masonry
This is the stone masonry type where stones employed are either undressed or roughly dressed. These masonry constructions do not have a uniform thickness. The strength of the rubble masonry is dependent on the:
- Quality of Mortar Used
- Use of Long through stones
- Proper filling of mortar between the stone spaces and joints
Rubble masonry can be again classified into
a. Coursed Rubble Masonry
b. Uncoursed Rubble Masonry
c. Dry Rubble Masonry
d. Polygonal Masonry
e. Flint Masonry
a. Coursed Rubble Masonry
In coursed rubble masonry construction, the stones in a particular course are in equal heights. The stones hence used possess different sizes. In this type, all the courses do not have same height. This type is commonly employed in the construction of public buildings, abutments, residential buildings and piers of ordinary bridges.
b. Uncoursed Rubble Masonry
An uncoursed rubble masonry is the cheapest and roughest form of stone masonry construction. These construction use stones of varied shape and size. The stones are directly taken from the quarry called as undressed stone blocks. The courses is not maintained regulary in this method of construction. Initially larger stones are laid first. The spaces between them are filled with spalls or sneeks. This is divided into two types:
- Random Uncoursed Rubble Masonry
- Square Uncoursed Rubble Masonry
Random Uncoursed Rubble Masonry: In this type, the weak corners and edges of the stone are removed with the help of a mason’s hammer. At the quoins and jambs, bigger stones are employed in order to increase the strength of the masonry.
Square Uncoursed Rubble Masonry: Here, the stones are made roughly square shape and used in construction. The facing stones are provided a hammer-dressed finish. Larger stones are used as quoins. Chips are not used as bedding.
c. Polygonal Rubble Masonry
Here, the stones for masonry are roughly shaped into irregular polygons. The stones are then arranged in such a way that it avoids vertical joints in the face work. Break the joints as possible. Use of stone chips to support the stones.
d. Flint Rubble Masonry
In areas where flint is available plenty, a flint rubble masonry is employed. Flints are irregularly shaped nodules of silica. They are extremely hard but brittle in nature. The thickness of the flintstones varies from 8 to 15cm. Their length varies from 15 to 30cm.
e. Dry Rubble Masonry
These are rubble masonry construction performed without the use of mortar. Small spaces are filled with smaller stone pieces. It is used in pitching the earthen dams and the canal slopes.
2. Ashlar Masonry
Ashlar masonry is constructed using accurately dressed stones that possess uniform and fine joints. The thickness of the joints ranges about 3mm which is arranged in various patterns. The size of the stone blocks must be in proportion with the thickness of the walls.
The various types of ashlar masonry are:
- Ashlar Fine Masonry
- Ashlar Block in Course
- Ashlar Chamfered Masonry
- Ashlar Rough Tooled Masonry
- Rock or Quarry Faced Masonry
1. Ashlar Fine Masonry
In ashlar fine masonry construction, each stone is cut into uniform size and shape, almost rectangular in shape. This shape hence provides perfect horizontal and vertical joints with the adjacent stones. An ashlar fine masonry construction is very costly.
2. Ashlar Rough Masonry
This type has stones whose sides are finely chisel -dressed. The face of the stones is made rough by means of tools. Around the perimeter of the rough dressed face of each stone, a strip of 25mm width is provided.
3. Rock and Quarry Faced
This masonry type has a 25 mm wide strip made by a chisel placed around the perimeter of every stone. The remaining portion of the face is left in the same form as it is received.
4. Ashlar Block in Course Masonry
This type is a combination of ashlar masonry and rubble masonry. The faces work of the masonry stones is either rough tooled or hammer dressed stones. The backing of the wall may be done in rubble masonry.
5. Ashlar Chamfered Masonry
A strip is provided as shown in the figure below. But the sides are chamfered or beveled at an angle of 45 degrees by means of a chisel at a depth of 25mm.