Stone Masonry is a craft of arranging stones of desired shape to form a structure. This process of construction has been employed for thousands of years and has a great history. There are numerous design patterns in the stone masonry process, and coursed rubble masonry is one among them, where the stones are arranged in a pattern with stones either undressed or roughly dressed. They are widely popular in rural areas and provide a good appearance to the structure. Here we take a look at coursed rubble stone masonry and everything you need to know about it, including the properties, applications, pros and cons.
What is coursed rubble stone masonry?
Coursed rubble stone masonry is the process of arranging stones in horizontal layers at certain intervals. The stones used in coursed rubble masonry are hammer-dressed and are of equal heights; however, the sizes differ by course. These types of stone masonry are used for the construction of residential buildings, boundary walls, warehouses, and more.
Properties of coursed rubble stone masonry
Size & Shape
The size of the stone that is used for coursed rubble stone masonry should not be less than 15 cm. The shape of the stones should not have a rounded surface. The stones are hammer-dressed on top, bed, and on the sides to make it compatible for laying close to other stones in the course.
Compressive Strength
The stones used for coursed rubble stone masonry should be hard, sound, and durable. It should have a compressive strength of at least 104.9 MPa.
Aesthetics
As the stones are hammer-dressed they have a rough texture that looks more balanced between rustic and architecturally pleasing.
Wall Dimensions
Generally, stone walls have a thickness ranging from 30 centimeters to 60 centimeters. The stone chosen for coursed rubble stone masonry should not be more than ¾ of the thickness of the wall. The horizontal courses of the stone wall should be of equal sizes; however, it can vary for different courses.
Construction Process in Coursed Rubble Stone Masonry
Selecting the stones
The stones can be selected from the quarries that are suitable for the construction. The stones should be of uniform color, quality, and texture, and should be clear from impurities and other deleterious materials. Stones that have a round face should not be selected.
Testing of stones
The selected stones are tested in the lab and should pass the compression and water absorption test. The stones should possess a compressive strength of not less than 300 kg/cm² and should not absorb water in excess of 5%. The size of the stones should be not less than 15 cm and not more than 3/4 of the thickness of the wall.
Dressing
Each stone is hammer-dressed on the face to remove uneven edges and sides, making it suitable to be laid close to neighbouring stones. The dressing process removes the bushes of more than 40 mm on the exposed face and 10 mm on the plastered face.
Preparing the mortar
A mixture of cement, sand, or lime is mixed to form a dry mixture of a standard ratio. The dry mixture is then mixed with water to bring it to a consistency for binding.
Laying Stones
All the stones should be wetted before laying. The wetted stones are laid close to the neighbouring stones. Ensure that the mortar joints that bind the stones are not more than 20 mm. The joints are monitored properly, and a wooden mallet is used to position the stone firmly. The levels of the horizontal courses can be adjusted using stones of similar height and mortar.
Joints
Stones are laid in a way that all the joints are fully packed with mortar and stones. The face joints should not be more than 12 mm thick and can be flushed and finished. The top portion of the structure is finished with mortar and small stone pieces.
Quoins
The quoins can be dressed and placed at the correct angle, which is approximately the same height as that of the course. They can be laid with a header and stretcher in the alternate courses.
Curing
The masonry work that uses cement is constantly kept moist for a minimum period of one week, for complete curing. The structure should be protected from rain, as it may damage the construction from mortar dropping and other damages.
Advantages and Disadvantages of coursed rubble stone masonry
Advantages
- The stones are hammer & chisel-dressed and are perfectly shaped to lay close to the other stones in the course.
- These bricks are strong, hard, and have high durability.
- They are eco-friendly as they don’t need steel or cement.
- These bricks can carry heavy loads and have high compressive strength.
- They give both a rough and aesthetic look to the structure.
Disadvantages
- They can be subject to damage or collapse when stones are not bound correctly.
- They have poor abrasion resistance against water, which could wash away the mortar and other fine materials.
- Cracks can develop within the structure if subjected to excessive weight and external stress.
- The stones are too heavy and transporting costs and labor needs can be high.
- The construction of coursed rubble stone masonry is time-consuming.
- Rainy and frost climatic conditions can penetrate through pores, leading to cracks.
Applications of coursed rubble stone masonry
- These masonry works are used for the construction of modern residential buildings, public buildings, hospitals, and schools.
- They are used for low-height walls, compounds and boundary walls.
- They are primarily used for laying the foundations of a structure that requires high load-bearing capacity.
- They are also used to build piers in ordinary bridges.
Conclusion
Coursed rubble stone masonry is widely applicable in construction projects that require a more balanced structure. They are both rough and the same way aesthetically pleasing. They can load heavy loads and are durable for a long period of time. These masonry works although requiring skilled labor, have a very low chance of failure. They are reliable for low-height walls, modern residential houses and other commercial structures.