SECTION I. CHARACTERISTICS OF BRICK
PHYSICAL PROPERTIES AND CLASSIFICATION
9-2. Structural clay products includes brick, hollow tile of all types, and architectural terra cotta, but exclude thin wall tile, sewer pipe, flue linings, and drain tile.
BRICK MASONRY UNITS
9-3. Bricks are small masonry units that are either solid or cored but not more than 25 percent. They are kiln-fired (baked) from various clay and shale mixtures. The chemical and physical characteristics of the ingredients change considerably and combine with the kiln temperature to produce the brick in a variety of colors and hardnesses. The clay or shale pits in some regions yield a product that is simply ground, moistened, formed, and baked into durable brick. In other regions, the clay or shale from several pits must be mixed to produce durable brick. Bricks are small enough to place with one hand. Uniform units can be laid in courses with mortar joints to form walls of almost unlimited length and height.
BRICK SIZES AND WEIGHT
9-4. Standard United States (US) bricks are 2 1/4 by 3 3/4 by 8 inches actual size. They may have three core holes or ten core holes. Modular US bricks are (2 2/3 by 4 by 8 inches) nominal size, normally having three core holes. English bricks are 3 by 4 1/2 by 9 inches, Roman bricks are 1 1/2 by 4 by 12 inches, and Norman bricks are 2 3/4 by 4 by 12 inches nominal size. Actual brick dimensions are smaller, usually by an amount equal to mortar joint width. Brick weighs from 100 to 150 pounds per cubic foot, depending on its ingredients and firing duration. Well-burned brick is heavier than underburned brick.
9-5. Sometimes you must cut a brick into various shapes to fill in spaces at corners and other locations where a full brick does not fit. Figure 9-1 shows the more common cut shapes: half or bat, three-quarter closure, quarter closure, king closure, queen closure, and split.
Figure 9-1. Common cut brick shapes
9-6. The five surfaces of a brick are called face, side, cull, end, and beds as shown in Figure 9-2.
Figure 9-2. Names of brick surfaces
9-7. The three general types of structural brick-masonry units are solid, hollow, and architectural terra cotta. All three can serve a structural function, a decorative function, or a combination of both. The three types differ in their formation and composition, and are specific in their use. Bricks commonly used in construction are--
Building bricks. Also called common, hard, or kiln-run bricks, these bricks are made from ordinary clays or shales and fired in kilns. They have no special scoring, markings, surface texture, or color. Building bricks are generally used as the backing courses in either solid or cavity brick walls because the harder and more durable kinds are preferred.
Face bricks. These are better quality and have better durability and appearance than building bricks because they are used in exposed wall faces. The most common face brick colors are various shades of brown, red, gray, yellow, and white.
Clinker bricks. These bricks are oven-burnt in the kiln. They are usually rough, hard, durable, and sometimes irregular in shape.
Pressed bricks. These bricks are made by the dry-press process rather than by kiln-firing. They have regular smooth faces, sharp edges, and perfectly square corners. Ordinarily, they are used as face bricks.
Glazed bricks. These have one surface coated with a white or other color of ceramic glazing. The glazing forms when mineral ingredients fuse together in a glass-like coating during burning. Glazed brick is particularly suited to walls or partitions in hospitals, dairies, laboratories, and other structures requiring sanitary conditions and easy cleaning.
Fire bricks. These are made from a special type of fire clay to withstand the high temperatures of fireplaces, boilers, and similar constructions without cracking or decomposing. Fire brick is generally larger than other structural brick, and often is hand-molded.
Cored bricks. These bricks have ten holes (two rows of five holes each) extending through their beds to reduce weight. Walls built from all cored bricks are not much different in strength than walls built from all solid bricks, and both have about the same resistance to moisture penetration. Whether cored or solid, use the more easily available brick that meets building requirements.
European bricks. Their strength and durability (particularly English and Dutch bricks) are about the same as US clay bricks.
Sand-lime bricks. These bricks are made from a lean mixture of slaked lime and fine sand containing a lot of silica. They are molded under mechanical pressure and hardened under steam pressure. These are used extensively in Germany.
STRENGTH OF BRICK MASONRY
9-8. The strength of a single brick masonry unit varies widely, depending on its ingredients and manufacturing method. The main factors governing the strength of brick masonry are:
9-9. Bricks can have an ultimate compressive strength as low as 1,600 psi, whereas some well-burned bricks have compressive strengths exceeding 15,000 psi.
9-10. Brick masonry laid with portland-cement-line mortar is stronger than an individual brick unit because this mortar is normally stronger than the brick. The load-carrying capacity of a wall or column made with plain lime mortar is much less than half that made with portland-cement-lime mortar. The compressive working strength of a brick wall or column laid with cement-lime mortar normally ranges from 500 to 600 psi.
9-11. In order for mortar to bond to brick, sufficient water must be present to completely hydrate the portland cement in the mortar. Bricks sometimes have high absorption and, if not corrected, will suck the water out of the mortar preventing complete hydration. A field test to determine if the brick has absorptive qualities is as follows: Using a medicine dropper, place 20 drops of water in a 1-inch circle (about the size of a quarter). If the brick absorbs all the water in less than 1 1/2 minutes, then it will suck the water out of the mortar when laid. To correct this condition, thoroughly wet the bricks and allow time for the surfaces to air-dry before placing.
9-12. A brick's resistance to weathering depends almost entirely upon its resistance to water penetration, because freeze-thaw action is almost the only type of weathering that affects it.
9-13. A brick wall made with superior workmanship will resist rain water penetration during a storm lasting as long as 24 hours accompanied by a 50 to 60 mile per hour wind.
9-14. Two important factors in preventing water penetration are tooled-mortar joints and caulking around windows and door frames. Mortar joints that bond tightly to the brick resist moisture penetration better than joints with loose bonds. Slushing or grouting the joints after laying the brick does not fill the joint completely. Fill the joints between the brick solidly, especially in the face tier. Tool the joint to a concave surface before the mortar sets up. When tooling, use enough force to press the mortar tightly against the brick on both sides of the joint. Although good bricklaying workmanship does not permit water penetration, it provides some means of removing moisture that does penetrate the masonry, such as properly designed flashing or the use of cavity walls.
9-15. Table 9-1 gives the hours of fire resistance for various thicknesses of brick walls determined by tests conducted on brick walls laid with portlandcement-lime mortar. The ASTM standard method for conducting fire tests was used.
Table 9-1. Fire resistance of brick load-bearing walls laid with portland-cement-lime mortar
9-16. A brick's resistance to abrasion depends largely upon its compressive strength, which is determined by how well it was fired. Well-burned brick has excellent wearing qualities.
INSULATING QUALITIES OF BRICK MASONRY
9-17. A brick masonry wall expands and contracts with temperature change. However, because the wall itself takes up a lot of the expansion and contraction, the amount of movement calculated theoretically does not actually occur. Therefore, walls up to 200 feet long do not need expansion joints, but longer walls require one expansion joint for every 200 feet.
9-18. Solid-brick masonry walls provide very little insulation from heat and cold. A cavity wall or a brick wall backed with hollow clay tile gives much better insulating value.
9-19. Brick walls are massive and provide good sound insulation. Generally, the heavier the wall, the better its sound-insulating value. However, the sound insulation provided by a wall more than 12 inches thick is not much greater than a wall 10 to 12 inches thick. Dividing a wall into two or more layers, such as a cavity wall, increases its resistance to sound transmission from one side of the wall to the other. Brick walls poorly absorb sound originating within the walls and reflect much of the sound back into the structure. However, impact sounds, such as a hammer striking the wall, travel a long way along the wall.
|David L. Heiserman, Editor||
Copyright © SweetHaven
Revised: June 06, 2015