masonry

A mason laying mortar on top of a finished course of blocks, prior to placing the next course.

Masonry is the building of structures from individual units laid in and bound together by mortar (though the word "masonry" sometimes means the stones, rather than the act or art of building, particularly in the expression "falling masonry" used in reports of fires and earthquakes). The common materials of masonry construction are brick, stone such as marble, granite, travertine, limestone; concrete block, glass block, and tile. Masonry is generally a highly durable form of construction. However, the materials used, the quality of the mortar and workmanship, and the pattern the units are put in can strongly affect the durability of the overall masonry construction.

Applications

A brick wall built using Flemish Bond

Masonry is commonly used for the walls of buildings, retaining walls and monuments. Brick is the most common type of masonry and may be either weight-bearing or a veneer. Concrete block masonry is rapidly gaining in popularity as a comparable material. Blocks - most of which have hollow cores - offer various possibilities in masonry construction, generally providing great compressive strength, and they're generally 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 materials such as brick and stone can increase the thermal mass of a building, giving increased comfort in the heat of summer and the cold of winter and can be ideal for passive solar applications.
• Brick typically will not require painting and so can provide a structure with reduced life-cycle costs, although sealing appropriately will reduce potential spalling due to frost damage. Concrete block of the non-decorative variety generally is painted or stuccoed if exposed.
• The appearance, especially when well crafted, can impart an impression of solidity and permanence.
• Is very heat resistant and thus will provide good fire protection

Disadvantages

• Extreme weather may cause degradation of the surface due to frost damage. This type of damage is common with certain types of brick, though relatively rare with concrete block. If non-concrete (clay-based) brick is to be used, care should be taken to select bricks suitable for the climate in question.
• Masonry must be built upon a firm foundation (usually reinforced concrete) to avoid potential settling and cracking. If expansive soils (such as adobe clay) are present, this foundation may need to be quite elaborate and the services of a qualified structural engineer may be required.
• The high weight increases structural requirements, especially in earthquake prone areas.

Structural limitations

Masonry boasts an impressive compressive strength (vertical loads) but is much lower in tensile strength (twisting or stretching) unless reinforced. The tensile strength of masonry walls can be strengthened by thickening the wall, or by building masonry "piers" (vertical columns or ribs) at intervals. Where practical, steel reinforcement also can be introduced vertically and/or horizontally to greatly increase tensile strength, though this is most commonly done with poured walls. (See Prestressed concrete.)

Veneer masonry

Brick veneer construction has strength imparted by a framework of wood or a rough masonry wall of other material over which is placed a layer of bricks for weatherproofing and providing a finished appearance. The brick veneer wall is connected to the structural walls by "brick ties", metal strips that are attached to the structural wall as well as the mortar joints of the brick veneer wall. There is typically an air gap between the brick veneer wall and the structural wall. As clay brick is not completely waterproof, the structural wall has a water-resistant surface (usually tar paper) and weep holes are left at the base of the brick veneer wall to ventilate the air gap.

Most insulated buildings that utilize concrete block, brick, veneers or some combination thereof feature interior insulation in the form of fiberglass batts between wooden wall studs or 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

Dry set masonry supports a rustic log bridge, where it provides a well-drained support for the log (this will increase its service life).

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 forego mortar all together.

See also: Dry-stone wall

Solid masonry

Solid masonry, without steel reinforcement, tends to have very limited applications in modern wall construction. While such walls can be quite economical and suitable in some applications, susceptibility to earthquakes and collapse is a major issue. Solid unreinforced masonry walls tend to be low and thick as a consequence.

Brick

Solid brick masonry is made of two or more layers 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). There are no significant utilitarian differences between most bonds, but the appearance of the finished wall is affected. Vertically staggered bonds tend to be somewhat stronger and less prone to major cracking than a non-staggered bond.

Uniformity and rusticity

The selection of the brick used, especially for color, will affect the appearance of the final surface. In buildings built during the 1970s, a high degree of uniformity of brick and accuracy in masonry was typical. In later periods this style was thought to be too sterile, so attempts were made to emulate older, rougher work. Some brick surfaces are made to look particularly rustic by including "burnt" bricks, which have a darker color or an irregular shape. Others may use antique salvage bricks, or new bricks may be artificially aged by applying various surface treatments. The attempts at rusticity of the late 20th century have been carried forward by masons specializing in a free, artistic style, where the courses are intentionally not straight, instead weaving to form more organic impressions.

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 thickness 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 (CMU)s. 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 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" 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. 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.

Some concrete blocks are colored, and some employ a split face, a technique that results in two blocks being manufactured as one unit and later split into two. This gives the blocks a rough face replicating the appearance of natural, quarried stone, such as brownstone. Examples of splitface block - as well as other types of CMUs and brick - can be seen here. For applications such as roadway sound control walls, the face patterns may be complex and even artistic.

A-Jacks

A-jacks (used in erosion walls and sea walls)are high 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

In the uniform placement pattern, each unit is in contact with the six adjacent units, providing high stability. They are patterned after the buckyball model^[1]

Stonework

Main article: Stonemasonry

Stone blocks used in masonry can be "dressed" or "rough." 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 courses (rows of even height) through the careful selection or cutting of stones, but a great deal of stone masonry is uncoursed.

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" (oval shaped smooth 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 veneers are maturing in their popularity as an alternative to natural stones. Attractive natural stone has become more expensive in many areas and in some areas is practically unavailable. Manufactured-stone veneers are typically made from concrete. Natural stones from quarries around the world are sampled and recreated using moulds, aggregate, and colorfast pigments. To the casual observer there may be no visual difference between veneers of natural and manufactured stone.

Rustic use of sandstone of varying color and size	City wall in Worms, Germany	City wall in Worms, Germany	City wall in Valence, Drôme, France using river rock
From castle in Germany	From castle in France	From Heidelberg Castle	From Heidelberg Castle
Marble repair, Parthenon	Ancient stonework, Delphi

Gabions

Gabions are rectangular wire baskets, usually of zinc protected steel that are filled with fractured stone of medium size. These will act as a single unit and are stacked with set-backs 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.

Masonry Training

Stonemasonry is one of the oldest professions in the history of construction. As such it is regarded as a traditional skill, and is one which is in heavy demand.

Prospective stonemasons will learn the profession through apprenticeships or a traineeship that will last 3 to 4 years. There are City & Guilds stonemasonry courses available that combine college based theory training with practical learning.

Passive fire protection (PFP)

Masonry walls are subject to stringent bounding, and, are considered both "old" systems, meaning their use has been standardised over many decades and their performance under fire conditions is known and listed in "old" catalogues, such as DIN4102, BS476 and the Canadian National Building Code and "new" systems. Masonry walls can also use "new" methods in terms of their PFP classification, based on recent certification listings as opposed to old, governmentally sanctioned ones. Apart from the old, standardised systems every architect knows, there are "new" systems consisting, for instance, of foamed concrete as well as concrete that contains lightweight aggregates such as shale or even vermiculite. In PFP, masonry walls have major advantages, such as the endothermic effect of its hydrates, as in chemically bound water, as well as unbound moisture from the original mix design both for a concrete block itself and the mortar itself, as well as the poured concrete, if the hollow cores inside the blocks are filled. Also, the sheer mass of masonry walls acts as a natural heatsink to absorb photons during real fires and the fire-testing upon which bounding is based. This makes for extremely reliably and solid, well documented passive fire protection, much less affected by onsite errors than drywall systems of equal fire-resistance ratings. When firestop mortars are used inside masonry wall service penetration firestops, heat is readily absorbed away from penetrants and into the surrounding structure, which keeps the unexposed side cool during a fire. Even though firestops may at times use purpose-made firestop mortars (which is quite different from the structural mortars used to lay up bricks and blocks), the trade jurisdiction for firestop mortars, as well as all other firestops on unionised construction sites lies with the Insulators, not the bricklayers, who are restricted to the mortar joints or "beds" between individual bricks or blocks, rather than service penetration firestops, which are not included in their apprenticeship programs.

See also

External links

Wikimedia Commons has media related to:

Masonry

• International Union of Bricklayers and Allied Craftworkers
• International Masonry Institute
• Masonry Advisory Council
• National Concrete Masonry Association

References

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