Masonry refers to building of structures from individual units laid in and bound together by mortar. The common materials of masonry construction are brick, stone, marble, granite, travertine, limestone, cast stone, concrete block, glass block, stucco, tile, and cob. Masonry is generally a highly durable form of construction. However, the materials used, the quality of the mortar and workmanship, and the pattern in which the units are assembled can significantly affect the durability of the overall masonry construction.

 

Applications

 

Masonry  is commonly used for the walls of buildings, retaining walls and buildings. Brick and concrete block are the most common types of masonry in use in industrialized nations and may be either weight-bearing or a veneer. Concrete blocks, especially those with hollow cores, offer various possibilities in masonry construction. They generally provide great compressive strength, and are best suited to structures with light transverse loading when the cores remain unfilled. Filling some or all of the cores with concrete or concrete with steel reinforcement (typically rebar) offers much greater tensile and lateral strength to structures.

 

Advantages

• The use of material such as bricks and stones can increase the thermal mass of a building and can protect the building from fire.

• Most types of masonry typically will not require painting and so can provide a structure with reduced life-cycle costs.

• Masonry is non-combustible product.

• Masonry walls are more resistant to projectiles, such as debris from hurricanes or tornadoes.

• Masonry structures built in compression preferably with lime mortar can have a useful life of more than 500 years as compared to 30 to 100 for structures of steel or reinforced concrete.

 

Disadvantages

• Extreme weather, under certain circumstances, can cause degradation of masonry wall surfaces due to frost damage.

• Masonry tends to be heavy and must be built upon a strong foundation, such as reinforced concrete, to avoid settling and cracking.

• Other than concrete, masonry construction does not lend itself well to mechanization, and requires more skilled labor than stick-framing.

• Masonry consists of loose components and has a low tolerance to oscillation as compared to other materials such as reinforced concrete, plastics, wood, or metals.

 

Structural limitations

 

Masonry has high compressive strength under vertical loads but has low tensile strength (against twisting or stretching) unless reinforced. The tensile strength of masonry walls can be increased by thickening the wall, or by building masonry piers (vertical columns or ribs) at intervals. Whenever practical, steel reinforcements such as windposts can be added.

 

Veneer masonry

 

A masonry veneer wall consists of masonry units, usually clay-based bricks, installed on one or both sides of a structurally independent wall usually constructed of wood or masonry. In this context the brick masonry is primarily decorative, not structural. The brick veneer is generally connected to the structural wall by brick ties (metal strips that are attached to the structural wall, as well as the mortar joints of the brick veneer). There is typically an air gap between the brick veneer and the structural wall. As clay-based brick is usually not completely waterproof, the structural wall will often have a water-resistant surface (usually tar paper) and weep holes can be left at the base of the brick veneer to drain moisture that accumulates inside the air gap. Concrete blocks, real and cultured stones, and veneer adobe are sometimes used in a very similar veneer fashion.

 

Most insulated buildings that utilize concrete block, brick, adobe, stone, veneers or some combination thereof feature interior insulation in the form of rigid insulation boards covered with plaster or drywall. In most climates this insulation is much more effective on the exterior of the wall, allowing the building interior to take advantage of the aforementioned thermal mass of the masonry. This technique does, however, require some sort of weather-resistant exterior surface over the insulation and, consequently, is generally more expensive.

 

Dry set masonry

 

The strength of a masonry wall is not entirely dependent on the bond between the building material and the mortar; the friction between the interlocking blocks of masonry is often strong enough to provide a great deal of strength on its own. The blocks sometimes have grooves or other surface features added to enhance this interlocking, and some dry set masonry structures forgo mortar altogether.

 

Brick

 

Solid brickwork is made of two or more wythes of bricks with the units running horizontally (called stretcher bricks) bound together with bricks running transverse to the wall (called "header" bricks). Each row of bricks is known as a course. The pattern of headers and stretchers employed gives rise to different bonds such as the common bond (with every sixth course composed of headers), the English bond, and the Flemish bond (with alternating stretcher and header bricks present on every course). Bonds can differ in strength and in insulating ability. Vertically staggered bonds tend to be somewhat stronger and less prone to major cracking than a non-staggered bond.

 

Serpentine masonry

 

A crinkle-crankle wall is a brick wall that follows a serpentine path, rather than a straight line. This type of wall is more resistant to toppling than a straight wall; so much so that it may be made of a single wythe of unreinforced brick and so despite its longer length may be more economical than a straight wall.

 

Concrete block

 

Blocks of cinder concrete (cinder blocks or breezeblocks), ordinary concrete (concrete blocks), or hollow tile are generically known as Concrete Masonry Units (CMUs). They usually are much larger than ordinary bricks and so are much faster to lay for a wall of a given size. Furthermore, cinder and concrete blocks typically have much lower water absorption rates than brick. They often are used as the structural core for veneered brick masonry, or are used alone for the walls of factories, garages and other industrial-style buildings where such appearance is acceptable or desirable. Such blocks often receive a stucco surface for decoration. Surface-bonding cement, which contains synthetic fibers for reinforcement, is sometimes used in this application and can impart extra strength to a block wall. Surface-bonding cement is often pre-colored and can be stained or painted thus resulting in a finished stucco-like surface.

 

The primary structural advantage of concrete blocks in comparison to smaller clay-based bricks is that a CMU wall can be reinforced by filling the block voids with concrete with or without steel rebar. Generally, certain voids are designated for filling and reinforcement, particularly at corners, wall-ends, and openings while other voids are left empty. This increases wall strength and stability more economically than filling and reinforcing all voids. Typically, structures made of CMUs will have the top course of blocks in the walls filled with concrete and tied together with steel reinforcement to form a bond beam. Bond beams are often a requirement of modern building codes and controls. Another type of steel reinforcement, referred to as ladder-reinforcement, can also be embedded in horizontal mortar joints of concrete block walls. The introduction of steel reinforcement generally results in a CMU wall having much greater lateral and tensile strength than unreinforced walls.

CMUs can be manufactured to provide a variety of surface appearances. They can be colored during manufacturing or stained or painted after installation. They can be split as part of the manufacturing process, giving the blocks a rough face replicating the appearance of natural stone, such as brownstone. CMUs may also be scored, ribbed, sandblasted, polished, striated (raked or brushed), include decorative aggregates, be allowed to slump in a controlled fashion during curing, or include several of these techniques in their manufacture to provide a decorative appearance.

 

 

A-jacks

 

A-jacks (used in erosion control walls and sea walls) are highly stable, concrete 6-pronged armor units designed to interlock into a flexible, highly permeable matrix. They can be installed either randomly or in a uniform pattern. They look like giant 3-foot versions of the metal jacks that children play with.

 

Stonework

 

Stone blocks used in masonry can be dressed or rough, though in both examples: corners, door and window jambs, and similar areas are usually dressed. Stone masonry utilizing dressed stones is known as ashlar masonry, whereas masonry using irregularly shaped stones is known as rubble masonry. Both rubble and ashlar masonry can be laid in coursed rows of even height through the careful selection or cutting of stones, but a great deal of stone masonry is uncoursed.

• Slipform stonemasonry produces a hybrid wall of reinforced concrete with a rubble stone face.

• Natural stone veneers over CMU, cast-in-place, or tilt-up concrete walls are widely used to give the appearance of stone masonry.

• Sometimes river rock of smooth oval-shaped stones is used as a veneer. This type of material is not favored for solid masonry as it requires a great amount of mortar and can lack intrinsic structural strength.

• Manufactured-stone, or cultured stone, veneers are popular alternatives to natural stones.

• Manufactured-stone veneers are typically made from concrete.

• Natural stones from quarries around the world are sampled and recreated using molds, aggregate, and colorfast pigments.

• To the casual observer there may be no visual difference between veneers of natural and manufactured stone.

 

Gabions

 

Gabions are rectangular wire baskets, usually of zinc-protected steel (galvanized steel) that are filled with fractured stone of medium size. These will act as a single unit and are stacked with setbacks to form a revetment or retaining wall. They have the advantage of being both well drained and flexible, and so resistant to flood, water flow from above, frost damage, and soil flow. Their expected useful life is only as long as the wire they are composed of and if used in severe climates (such as shore-side in a salt water environment) must be made of appropriate corrosion-resistant wire.

 

Bagged concrete

 

A low grade concrete may be placed in woven plastic sacks similar to that used for sandbags and then emplaced. The sacks are then watered and the emplacement then becomes a series of artificial stones that conform to one another and to adjacent soil and structures. This conformation makes them resistant to displacement. The sack becomes non-functional and eventually disintegrates. This type of masonry is frequently used to protect the entrances and exits of water conduits where a road passes over a stream or dry wash. It is also used to protect stream banks from erosion, especially where a road passes close by.

 

Bricks and Brick making

 

A brick is a block or a single unit of a kneaded clay-bearing soil, sand and lime, or concrete material, fire-hardened or air-dried, used in masonry construction. Lightweight bricks (also called "lightweight blocks") are made from expanded clay aggregate. Fired bricks are the most numerous type and are laid in courses and numerous patterns known as bonds, collectively known as brickwork, and may be laid in various kinds of mortar to hold the bricks together to make a durable structure.  Bricks are produced in numerous classes, types, materials, and sizes which vary with region and time period, and are produced in bulk quantities. Two basic categories of bricks are fired and non-fired bricks. Fired bricks are one of the longest-lasting and strongest building materials, sometimes referred to as artificial stone, and have been used since circa 5000 BC. Air-dried bricks have a history older than fired bricks, are known by the synonyms mud brick and adobe, and have an additional ingredient of a mechanical binder such as straw.

 

Clay Preparation

 

Tempering

 

Tempering is adding water to the clay soil in order to make it more workable. Too much water added to the clay mix will decrease quality, though.

 

Disintegration and Crushing

 

An alternative to tempering is disintegration or weathering, which involves allowing clay to dry in the sun and accept moisture from rain and dew. The repeated drying and moistening of clay will bring clay to a plasticity and workability appropriate for brickmaking. Crushing will make the mixture more homogeneous.

 

Mixing

 

Mixing is done to make the clay soil homogeneous and smooth. There are different techniques that can be used to do this, including using animal power or letting humans mix the clay with their feet. Different admixtures such as coal or sawdust can be added to the clay for two beneficial reasons: 1) reduce cracking during drying and 2) reduce fuel usage during firing.

 

Molding

 

Bricks should have standard characteristics if they are to be used in construction. For example, contractors may buy bricks from several different sources for one project: the bricks must be the same size or there will be problems matching the construction of different sections of the building. Moreover, a standard brick size will allow a contractor to more accurately determine how many bricks will be needed for a project. A new brickmaker, therefore, should follow local standards, checking with other brickmakers in the area or with local authorities or construction contractors.

 

Shrinkage

 

When determining the size of a mold for brickmaking, a necessary consideration must be shrinkage. Bricks will shrink when drying, so the mold size must be larger than the intended finished brick.

 

Slop Molding

 

In slop molding, a wet clay mixture is used- the mix is put into a rectangular form without a top or bottom. A problem with this technique is that because the mix is so wet, the brick may deform under its own weight and the surface can be marked easily.

 

Sand Molding

 

Sand molding utilizes a drier clay mix, formed into a wedge and thrown into a mold. A bow cutter will be used to smooth the top of the brick, and the form will can be released because of a hinged bottom. Since the clay is drier, the brick can be moved with wooden palettes which can reduce the amount of surface marks. There are multiple benefits to using sand molding instead of slop molding, such as:

• Less water is used, so there is less cracking and the bricks are stronger.

• Fewer molds are needed because they can be removed from the brick right away.

• The work space is cleaner because of less splashing of the drier mix.

• The worker is standing up instead of squatting down, so they are more comfortable.

• The bricks are more regular because they don't deform like slop molded bricks, so a better product is produced. Therefore, better construction and better looking buildings will be possible.

• Slop molded bricks can be imprinted with the brickmaker's name, called a "frog," on the flat side of the brick. This helps the brick dry and fire better, and is a good form of advertising.

 

Drying

 

Water was added during clay preparation to increase workability of the mixture, but in drying it is removed for several reasons. First, there will be less cracking in fired bricks with less water content. Second, additional fuel is needed, beyond what is used for firing, to dry the bricks in the kiln. Proper drying of bricks will involved rotating the bricks for different exposures to ensure even drying rates.

 

For best results, drying should be done slowly. This will help with more even drying. Also, the best drying technique may change from location to location, so the brickmakers must gain experience to determine the best way to dry bricks for each production process.

 

Firing

 

Laying out and constructing a clamp

A clamp is a field kiln built from the green bricks that will be fired. Clamps vary with size and shape and must be oriented with respect to wind direction. Once a clamp is laid out and constructed, it must be insulated.

 

Finally, the process of firing the clamp will take place in several steps. First, pre-heating, or water-smoking, will remove the water leftover from the drying process. This process is still physical. The second stage is firing, where the clay bricks will vitrify through a chemical process. The temperature must remain constant at this stage for complete vitrification. Finally, for the cooling stage, the temperature must be slow and steady. A clamp may take two weeks to cool.