LOAD BEARING MASONRY
Load bearing masonry is among the oldest and most widespread building techniques in the world. The earliest load bearing masonry consisted to stones stacked one over the other. Over the passage of time, the stones were chiseled and dressed to make more stable masonry walls. The firing of earth blocks gave rise to the earliest form of brick masonry. Over the centuries, masonry has evolved into a precise science with a myriad of options in materials and styles. Some of the more common load bearing masonry used today is brick, stone and concrete masonry units (CMU) or concrete blocks. Among these there are several varieties depending on the materials and system of laying the masonry units. Some of the more recent advancements are aerated concrete blocks, hollow concrete blocks, autoclaved ceramic blocks etc.
Masonry can be classified in the following manner:
- Material: Stone, brick, block
- Cavity or non cavity
- Reinforced or non-reinforced
- Composition: one material or composite
Masonry typically involves the laying the masonry unit (MU) one layer at a time. A mortar is used to hold the MUs in place and provide them with strength and stability. Mortars can be of several types but the broad classification would be cement mortars, lime mortars and synthetic adhesives. Earth is also used as mortar in some parts of the world.
Load bearing masonry by its nature, is a time consuming construction technique. Laying brick after brick, course upon course is a tedious process. The advent of panelized systems, load bearing masonry began to lose favor with home builders in the industrialized world. Advancements such as quick setting mortars have helped quicken the process. Attempts to mechanize the masonry process by using brick laying robots have met with limited success and skilled masons remain valued the world over. Another attempt at speeding up the masonry process has been through the use of mortarless masonry or dry masonry. This type of masonry uses factory made interlocking blocks that can be laid without the use of mortar.
There has been a recent resurgence in the use of load bearing masonry as more and more users have begun to recognize its advantages. Masonry is seen as a symbol of permanence and solidity. It is highly fire resistant and has a high compressive strength. In addition to this the appearance and texture of masonry is preferred by many and the innumerable patterns possible in masonry make it a popular construction technique.
The advantages of using load bearing masonry are:
- Load bearing masonry is solid and durable.
- It is fire resistant.
- There are several colors and textures available.
- The tools and implements used are simple and low-tech.
- Does not require a great deal of preparation or fabrication in advance.
- Load bearing masonry has high compressive strength.
- Aesthetically attractive.
The disadvantages of load bearing masonry are:
- A slow and tedious process.
- Requires skilled masons.
- Cost of bricks can make it unviable.
- Low tensile strength, can fail during earthquakes.
- Load bearing masonry, especially brick masonry is porous and needs to be protected from water.
- Load bearing masonry has a high self weight.
- It has poor thermal insulation properties.
The problem of high heat conductance can be reduced in the following ways:
- By providing air traps – double walls and rat trap bonds.
- Using insulation in the form of Exterior Insulation and Finish System (EIFS)
- Interior insulation such as batt insulation and stud walls.
- In-wall insulation made of polystyrene, vermiculite etc.
Building codes for load bearing masonry are well established and well documented. In the United States, the engineering design of masonry is governed by the American Concrete Institute and the American Society of Civil Engineers. All aspects of masonry are clearly listed and described. The code mandates that the thickness must be at least 6 inches in case of single story buildings and at least 8 inches for structures more than one story (Allen & Thallon, 2001).