Masonry
Masonry predates written history. Before anyone wrote down how to do it, people were already stacking stone and brick into walls that would outlast them. The craft built the Egyptian pyramids, raised Roman aqueducts, and pushed medieval cathedrals toward the sky. Yet the principle underneath all of it stays humble. A mason lays individual units of stone, brick, concrete, or similar material, and binds them with mortar. The person who does this work is a mason or bricklayer, or in some places a brickie, and both fall under the construction trades.
So why does something this ancient still shape the buildings around us? How does a wall made of loosely connected blocks, each only held to the next by a thin layer of mortar, manage to stand at all? Why does the same material that shrugs off fire and hurricane debris fail so badly in an earthquake? And how did a craft once defined by perfect uniformity swing back toward deliberate roughness? The answers run from the friction between two dry stones to the chemistry of water trapped inside a concrete block.
Each block or brick is only loosely connected to the next via a thin layer of mortar. Early structures used the weight of the masonry itself to stabilize against lateral movement, leaning on sheer mass rather than any strong bond. That reliance on weight is also the weakness. Because masonry walls depend mainly on their own weight to stay in place, they do not perform well in earthquakes, when entire buildings are shaken horizontally. Many collapses during earthquakes happen in buildings with load-bearing masonry walls, and the heavier the building, the more damage it tends to suffer.
The strength of a masonry wall, though, is not entirely about the bond between material and mortar. The friction between interlocking blocks is often enough to provide a great deal of strength on its own. Blocks sometimes carry grooves or other surface features added to enhance that interlocking. Some dry set masonry structures go further and forgo mortar altogether, letting friction do all the work.
Since the mid-20th century, masonry has often featured steel-reinforced elements. These carry the tension force present in modern thin, light, tall building systems, a job the old stack-and-weight method could never do. The way the units are assembled, the pattern itself, can substantially affect the durability of the whole.
Stone blocks can be dressed or rough, though corners, door and window jambs, and similar areas are usually dressed in both cases. Stonemasonry using dressed stones is known as ashlar masonry. Masonry using irregularly shaped stones is rubble masonry. Both can be laid in coursed rows of even height through careful selection or cutting of stones, but a great deal of stone masonry is uncoursed.
Slipform stonemasonry produces a hybrid wall: reinforced concrete with a rubble stone face. River rock, made of smooth oval-shaped stones, is sometimes used as a veneer, but it is not favored for solid masonry because it requires a great amount of mortar and can lack intrinsic structural strength. Natural stone veneers over concrete walls are widely used to give the appearance of stone masonry without the full mass.
Manufactured-stone, or cultured stone, veneers are popular alternatives to natural stone. These are typically made from concrete, with quarried stones from around the world 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.
A solid brickwork wall is made of two or more vertical layers, called wythes. Bricks running horizontally, the stretchers, are bound together with bricks running transverse to the wall, the headers. Each row is known as a course. The pattern of headers and stretchers gives rise to different bonds. The common bond places headers on every sixth course. The Flemish bond alternates stretcher and header bricks on every course, and the English bond is another arrangement entirely.
Bonds 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. The choice is not only structural but practical, shaping how a wall ages and where it might fail first.
A crinkle-crankle wall takes the logic somewhere unexpected. This brick wall follows a serpentine path rather than a straight line, and that curve makes it more resistant to toppling. It can be made of a single wythe of unreinforced brick. Despite its longer length, it may be more economical than a straight wall.
Buildings built during the 1950s to 1970s favored a high degree of uniformity of brick and accuracy in masonry. In the period since then, that style was thought to be too sterile, so attempts were made to emulate older, rougher work. The pendulum swung from precision back toward character.
Some brick surfaces are made to look particularly rustic by including burnt bricks, which have a darker color or an irregular shape. Others use antique salvage bricks. New bricks may be artificially aged through surface treatments such as tumbling. The goal in each case is to undo the machine-perfect look that an earlier generation had prized.
The rusticity of the late 20th century has been carried forward by masons specializing in a free, artistic style. In this work the courses are intentionally not straight. Instead they weave to form more organic impressions, turning a wall into something closer to a drawing in brick.
Concrete Masonry Units, or CMUs, include blocks of cinder concrete known as cinder blocks or breezeblocks, ordinary concrete blocks, and hollow tile. They are usually much larger than ordinary bricks, so they are much faster to lay for a wall of a given size. Cinder and concrete blocks also typically have much lower water absorption rates than brick. They serve as the structural core for veneered brick masonry or stand alone for factories, garages, and other industrial-style buildings.
The primary structural advantage of concrete blocks over smaller clay-based bricks lies in their voids. A CMU wall can be reinforced by filling the block voids with concrete, with or without steel rebar. Certain voids are designated for filling, particularly at corners, wall-ends, and openings, while others are left empty. This boosts strength more economically than filling every void. The top course is often filled with concrete and tied together with steel reinforcement to form a bond beam, frequently a requirement of modern building codes.
Architectural CMUs add appearance to function. They can be split during manufacturing to give a rough face replicating natural stone such as brownstone. They may also be scored, ribbed, sandblasted, polished, or striated. Glazed concrete masonry units bond a permanent colored facing of polyester resins, silica sand, and other chemicals to the block, providing a smooth impervious surface.
Masonry can withstand temperatures up to 1000 degrees Fahrenheit and direct exposure to fire for up to 4 hours. Concrete masonry keeps fires contained to their room of origin 93 percent of the time. For these reasons, concrete and masonry units hold the highest flame spread index classification, Class A. The protection comes partly from an endothermic effect of the hydrates, the chemically bound water, unbound moisture, and any poured concrete inside the filled cores. Fire cuts can be used to increase safety and reduce fire damage to masonry buildings.
The same mass that resists fire brings burdens. Masonry is heavy and must be built on stable ground, made of either undisturbed or mechanically compacted soil, or cracking may occur. Extreme weather can degrade masonry through the expansion and contraction forces of freeze-thaw cycles. Unlike concrete, masonry does not lend itself well to mechanization and requires more skilled labor.
Gabions handle a different problem. These are baskets, now usually of galvanized steel, filled with fractured stone of medium size. Stacked with setbacks, they act as a single unit to form a revetment or retaining wall. They are well drained, flexible, and resistant to flood and frost. Their useful life lasts only as long as the wire, so severe climates such as a salt water shore demand corrosion-resistant wire. Earlier gabions were often cylindrical wicker baskets, open at both ends, used for temporary military construction.
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Common questions
What is masonry in construction?
Masonry is the craft of building a structure with stone, brick, concrete, or similar material, often laid in, bound, and pasted together by mortar. The term can also refer to the building units themselves, such as stones, bricks, and concrete blocks.
What materials are used in masonry?
The common materials of masonry construction are bricks and building stone, including granite, marble, and limestone. Masonry also uses cast stone, concrete blocks, glass blocks, and adobe.
Why does masonry perform poorly in earthquakes?
Masonry walls rely mainly on their own weight to stay in place, with each block only loosely connected to the next by a thin layer of mortar. When a building is shaken horizontally during an earthquake, load-bearing masonry walls often collapse, and heavier buildings suffer more damage.
What is the difference between ashlar and rubble masonry?
Ashlar masonry uses dressed stones, while rubble masonry uses irregularly shaped stones. Both can be laid in coursed rows of even height through careful selection or cutting, though a great deal of stone masonry is uncoursed.
How fire resistant is masonry?
Masonry can withstand temperatures up to 1000 degrees Fahrenheit and direct exposure to fire for up to 4 hours. Concrete masonry keeps fires contained to their room of origin 93 percent of the time and holds the highest flame spread index classification, Class A.
What is a crinkle-crankle wall in masonry?
A crinkle-crankle wall is a brick wall that follows a serpentine path rather than a straight line. Its curve makes it more resistant to toppling, so it can be built from a single wythe of unreinforced brick and may be more economical than a straight wall despite its longer length.
What are concrete masonry units (CMUs)?
Concrete Masonry Units, or CMUs, are blocks of cinder concrete, ordinary concrete, or hollow tile that are usually much larger than ordinary bricks and faster to lay. Their voids can be filled with concrete and steel rebar to add tensile and lateral strength, often forming a bond beam at the top course.