The stone masonry has been in use from a very ancient times. The buildings constructed thousands years ago still stand today which shows the living example of durability and strength along with weather resisting qualities. The stone masonry has very high crushing strength due to which it is used in the construction of dams, piers, docks, and other marine structure.
The stone masonry can be classified into the following two types:
Ashlar masonry consists of carefully dressed stones with accurate bedding and fine joints of 3mm thick. This is the best type of stone construction. It is ensured that the sizes of individual stones are in conformity with the general proportions of the wall in which they are placed. It is further divided into the following types:
1. Ashlar Fine
In this type of masonry, stones are well dressed on all bed and side joints and the faces are rendered perfectly true to the desired pattern. The stones are laid in regular courses not less than 30 cm height. Almost all the courses are of same thickness. The face stones are laid headers and stretchers alternately. The height of stones used in never less than their breadth and their length never less than twice their height.
2. Ashlar Rough Tooled
In this type of masonry, the exposed faces of stones have a fine dressed chisel drafting all around the edges. This may be about 25 cm in width. The portions in between the drafts in roughly tooled. The thickness of joints allowed in this case be 6 mm. In all other respects it conforms to the specifications of Ashlar fine masonry.
3. Ashlar Rock Quarry Faced
In this type of masonry, The exposed face between the draft is not tooled but is left unfinished. The projections in the space enclosed by chisel drafts should not exceed 8 cm to 10 cm.
4. Ashlar Chamfered
In this case the edges round the exposed face of each stone are beveled off at an angle 45° for a depth of 25 mm or more.
5. Ashlar Facing
In this type of masonry, the faces of stones are rough tooled, rustic or chamfered and are provided in face work only but the backing may be made in brick work, concrete or rubble masonry. The stones are not less than 20 cm in height and 1 1/2 times the height in width. One third of the length of each course should be of headers. The bed joints of all the stones are dressed perfectly true and square. Bond stones should run through the backing when the wall is less than 80 cm in thickness. For greater thickness the bond stones should overlap each other by 15 cm.
6. Ashlar Block in Course
It is similar to ashlar rough tooled with the only difference that in this case the height of the course is lesser but not less than 20 cm.
In rubble masonry the stones are not of uniform size and shape and are not finely finished while constructing rubble masonry following points should be taken in mind:
1. Width of the face stone should not be less than the height of the course.
2. All the stones should be wetted before laying and stones from opposite faces should bond with each other.
3. The backing should have sufficient bond with facing. The stones on the face should have full joints for a specified distance from the face.
4. Sufficient headers should be used in each course.
5. The height of stone should not exceed its least horizontal dimension.
6. The stones should be placed on their widest side so that they may not act as edges. Further edged stones with in sufficient tails should not be used.
7. Chips should not be used in bed joints for setting the stones.
The rubble masonry is further classified into the following types:
1. Un-coursed Rubble Masonry
This type of masonry is built practically without any dressing. This is the poorest form of stone masonry. The stones used are taken directly from quarry. Larger stones are laid on flat beds. In this vertical joints are not formed to plumbness. The stones to be used for face should have uniform color and greater size. One stone is used for every square meter of face work. Bond stones provided to interlock the two faces should extend up to the full thickness of the wall if the wall is less than 60cm in thickness. A line of headers overlapping each other for a length of at least 15cm are laid right through the wall for more than 60cm thick walls. In this case the thickness of joints should not exceed 12mm.
2. Random Rubble Masonry
Random rubble masonry is slightly superior than un-coursed rubbled masonry. The stones to be used in this type are hammer or chisel dressed. The stones in each course need not be of same height. All the courses should be of same height. Not more than two stones, one above the other should be used in each course. The face of stones are of uniform color and approximately equal in size. The height of stones should not be more than its breadth or length of tail into the work. Small chips should be used when joints are very thick. At least one fourth of stones should tail back into the hearting for ensuring proper strength to the work.
3. Coursed Rubble Masonry
This type of masonry is further divided into 1st class, 2nd class and 3rd class masonry. It is commonly used in various types of residential and public buildings, piers and abutments of bridges. In the 1st class coursed rubble masonry all the courses are built to same height with minimum height being 15 cm. The beds of face stone are hammer or chisel dressed. In a good work, about one third of face stones tail back into hearting for a distance of two times their height for normal walls and three times for thicker walls. The thickness of joints should not exceed 10 mm.
4. Dry Rubble Masonry
In this type of masonry mortar is not used. It is constructed in same manner as ordinary rubble masonry.