Brick masonry is construction in which uniform units ("bricks"), small enough to be placed with one hand, are laid in courses with mortar joints to form walls. Bricks are kiln baked from various clay and shale mixtures. The chemical and physical characteristics of the ingredients vary considerably. These characteristics and the kiln temperatures combine to produce brick in a variety of colors and harnesses. In some regions, individual pits yield clay or shale which, when ground and moistened, can be formed and baked into durable brick. In other regions, clay or shale from several pits must be mixed.
Standard U.S. bricks are 2 1/4-by-3 3/4-by-8 inches nominal size. They may have three core holes or ten core holes. Modular U.S. bricks are 2 1/4-by-3 5/8-by-7 5/8 inches nominal size. They usually have 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 a mortar joint width. Bricks weigh from 100 to 150 pounds per cubic foot, depending on the ingredients and duration of firing. Fired brick is heavier than under-burned brick. The six surfaces of a brick are called cull, beds, side, end, and face, as shown in figure 8-30.
Figure 8-30.-Names of brick surfaces.
Occasionally you will have to cut brick into various shapes to fill in spaces at corners and other locations where a full brick does not fit. Figure 8-31 shows the more common cut shapes: half or bat, three-quarter closure, quarter closure, king closure, queen closure, and split.
Figure 8-31.-Common cut brick shapes.
TYPES OF BRICKS
Brick masonry units may be solid, hollow, or architectural terra cotta. All types can serve a structural function, a decorative function, or a combination of both. The various types differ in their formation and composition.
Building brick, also called common, hard, or kiln-run brick, is made from ordinary clay or shale and is fired in kilns. These bricks have no special shoring, markings, surface texture, or color. Because building bricks are generally used as the backing courses in either solid or cavity brick walls, the harder and more durable types are preferred.
Face brick is better quality and has better durability and appearance than building brick. Because of this, face bricks are used in exposed wall faces. The most common face brick colors are various shades of brown, red, gray, yellow, and white.
Clinker brick is over burned in the kiln. Clinker bricks are usually rough, hard, durable, and sometimes irregular in shape.
Pressed brick is made by a dry-press process rather than by kiln firing. Pressed bricks have regular smooth faces, sharp edges, and perfectly square corners. Ordinarily, they are used like face brick.
Glazed brick has one surface coated with a white or colored ceramic glazing. The glazing forms when mineral ingredients fuse together in a glass like coating during burning. Glazed bricks are particularly suited to walls or partitions in hospitals, dairies, laboratories, and other structures requiring sanitary conditions and ease of cleaning.
Fire brick is made from a special type of clay. This clay is very pure and uniform and is able to withstand the high temperatures of fireplaces, boilers, and similar constructions. Fire bricks are generally huger than other structural bricks and are often hand molded.
Cored bricks have ten holestwo rows of five holes each-extending through their beds to reduce weight. Walls built from cored brick are not much different in strength than walls built from solid brick. Also, both have about the same resistance to moisture penetration. Whether cored or solid, use the more available brick that meets building requirements.
European brick has strength and durability about equal to U.S. clay brick. This is particularly true of the English and Dutch types.
Sand-lime brick is made from a lean mixture of slaked lime and fine sand. Sand-lime bricks are molded under mechanical pressure and are hardened under steam pressure. These bricks are used extensively in Germany.
STRENGTH OF BRICK MASONRY
The main factors governing the strength of a brick structure include brick strength, mortar strength and elasticity, bricklayer workmanship, brick uniformity, and the method used to lay brick. In this section, well cover strength and elasticity. Workmanship is covered separately in the next section.
The strength of a single brick masonry unit varies widely, depending on its ingredients and manufacturing method. Brick can have an ultimate compressive strength as low as 1,600 psi. On the other hand, some well-burned brick has compressive strength exceeding 15,000 psi.
Because portland-cement-lime mortar is normally stronger than the brick, brick masonry laid with this mortar is stronger than an individual brick unit. The load-carrying capacity of a wall or column made with plain lime mortar is less than half that made with portland-cement-lime mortar. The compressive working strength of a brick wall or column laid with plain lime mortar normally ranges from 500 to 600 psi.
For mortar to bond to brick properly, sufficient water must be present to completely hydrate the
portland cement in the mortar. Bricks sometimes have high absorption rates, and, if not properly treated, can "suck" the water out of the mortar, preventing complete hydration. Here is a quick field test to determine brick absorptive qualities. Using a medicine dropper, place 20 drops of water in a l-inch circle (about the size of a quarter) on a brick. A brick that absorbs all the water in less than 1 1/2 minutes 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.
Good bricklaying procedure depends on good workmanship and efficiency. Efficiency involves doing the work with the fewest possible motions. Each motion should have a purpose and should accomplish a definite result. After learning the fundamentals, every Builder should develop methods for achieving maximum efficiency. The work must be arranged in such a way that the Builder is continually supplied with brick and mortar. The scaffolding required must be planned before the work begins. It must be built in such a way as to cause the least interference with other crewmembers.
Bricks should always be stacked on planks; they should never be piled directly on uneven or soft ground. Do not store bricks on scaffolds or runways. This does not, however, prohibit placing normal supplies on scaffolding during actual bricklaying operations. Except where stacked in sheds, brick piles should never be more than 7 feet high. When a pile of brick reaches a height of 4 feet, it must be tapered back 1 inch in every foot of height above the 4-foot level. The tops of brick piles must be kept level, and the taper must be maintained during unpiling operations.
To efficiently and effectively lay bricks, you must be familiar with the terms that identify the position of masonry units and mortar joints in a wall. The following list, which is referenced to figure 8-32, provides some of the basic terms you will encounter.
Figure 8-32.-Masonry units and mortar joints.
The term "bond" as used in masonry has three different meanings: structural bond, mortar bond, or pattern bond.
Structural bond refers to how the individual masonry units interlock or tie together into a single structural unit. You can achieve structural bonding of brick and tile walls in one of three ways:
Mortar bond refers to the adhesion of the joint mortar to the masonry units or to the reinforcing steel.
Pattern bond refers to the pattern formed by the masonry units and mortar joints on the face of a wall. The pattern may result from the structural bond, or may be purely decorative and unrelated to the structural bond. Figure 8-33 shows the six basic pattern bonds in common use today: running, common or American, Flemish, English, stack, and English cross or Dutch bond.
Figure 8-33.-Types of masonry bonds.
The running bond is the simplest of the six patterns, consisting of all stretchers. Because the bond has no headers, metal ties usually form the structural bond. The running bond is used largely in cavity wall construction, brick veneer walls, and facing tile walls made with extra wide stretcher tile.
The common, or American, bond is a variation of the running bond, having a course of full-length headers at regular intervals that provide the structural bond as well as the pattern. Header courses usually appear at every fifth, sixth, or seventh course, depending on the structural bonding requirements. You can vary the common bond with a Flemish header course. In laying out any bond pattern, be sure to start the corners correctly. In a common bond, use a three-quarter closure at the corner of each header course.
In the Flemish bond, each course consists of alternating headers and stretchers. The headers in every other course center over and under the stretchers in the courses in between. The joints between stretchers in all stretcher courses align vertically. When headers are not required for structural bonding, you can use bricks called blind headers. You can start the corners in two different ways. In the Dutch corner, a three-quarter closure starts each course. In the English corner, a 2-inch or quarter closure starts the course.
The English bond consists of alternating courses of headers and stretchers. The headers center over and under the stretchers. However, the joints between stretchers in all stretcher courses do not align vertically. You can use blind headers in courses that are not structural bonding courses.
The stack bond is purely a pattern bond, with no overlapping units and all vertical joints aligning. You must use dimensionally accurate or carefully rematched units to achieve good vertical joint alignment. You can vary the pattern with combinations and modifications of the basic patterns shown in figure 8-33. This pattern usually bonds to the backing with rigid steel ties or 8-inch-thick stretcher units when available. In large wall areas or load-bearing construction, insert steel pencil rods into the horizontal mortar joints as reinforcement.
The English cross or Dutch bond is a variation of the English bond. It differs only in that the joints between the stretchers in the stretcher courses align vertically. These joints center on the headers in the courses above and below.
When a wall bond has no header courses, use metal ties to bond the exterior wall brick to the backing courses. Figure 8-34 shows three typical metal ties.
Figure 8-34.-Metal ties.
Install flashing at any spot where moisture is likely to enter a brick masonry structure. Flashing diverts the moisture back outside. Always install flashing under horizontal masonry surfaces, such as sills and copings; at intersections between masonry walls and horizontal surfaces, such as a roof and parapet or a roof and chimney; above openings (doors and windows, for example); and frequently at floor lines, depending on the type of construction. The flashing should extend through the exterior wall face and then turn downward against the wall face to form a drop.
You should provide weep holes at intervals of 18 to 24 inches to drain water to the outside that might accumulate on the flashing. Weep holes are even more important when appearance requires the flashing to stop behind the wall face instead of extending through the wall. This type of concealed flashing, when combined with tooled mortar joints, often retains water in the wall for long periods and, by concentrating the moisture at one spot, does more harm than good.
MORTAR JOINTS AND POINTING
There is no set rule governing the thickness of a brick masonry mortar joint. Irregularly shaped bricks may require mortar joints up to 1/2 inch thick to compensate for the irregularities. However, mortar joints 1/4 inch thick are the strongest. Use this thickness when the bricks are regular enough in shape to permit it.
A slushed joint is made simply by depositing the mortar on top of the head joints and allowing it to run down between the bricks to form a joint. You cannot make solid joints this way. Even if you fill the space between the bricks completely, there is no way you can compact the mortar against the brick faces; consequently a poor bond results. The only effective way to build a good joint is to trowel it.
The secret of mortar joint construction and pointing is in how you hold the trowel for spreading mortar. Figure 8-35 shows the correct way to hold a trowel. Hold it firmly in the grip shown, with your thumb resting on top of the handle, not encircling it. If you are right-handed, pick up mortar from the outside of the mortar board pile with the left edge of your trowel (figure 8-36, view 1). You can pick up enough to spread one to five bricks, depending on the wall space and your skill. A pickup for one brick forms only a small pile along the left edge of the trowel. A pickup for five bricks is a full load for a large trowel (view 2).
Figure 8-35.-Correct way to hold a trowel.
Figure 8-36.-Picking up and spreading mortar.
If you are right-handed, work from left to right along the wall. Holding the left edge of the trowel directly over the center line of the previous course, tilt the trowel slightly and move it to the right (view 3), spreading an equal amount of mortar on each brick until you either complete the course or the trowel is empty (view 4). Return any mortar left over to the mortar board.
Do not spread the mortar for a bed joint too far ahead of layingfour or five brick lengths is best. Mortar spread out too far ahead dries out before the bricks become bedded and causes a poor bond (figure 8-37). The mortar must be soft and plastic so that the brick will bed in it easily. Spread the mortar about 1 inch thick and then make a shallow furrow in it (figure 8-38, view 1). A furrow that is too deep leaves a gap between the mortar and the bedded brick. This reduces the resistance of the wall to water penetration.
Figure 8-37.-A poorly bonded brick.
Figure 8-38.-Making a bed joint in a stretcher course.
Using a smooth, even stroke, cut off any mortar projecting beyond the wall line with the edge of the trowel (figure 8-38, view 2). Retain enough mortar on the trowel to butter the left end of the first brick you will lay in the fresh mortar. Throw the rest back on the mortar board.
Pick up the first brick to be laid with your thumb on one side of the brick and your fingers on the other (figure 8-39). Apply as much mortar as will stick to the end of the brick and then push it into place. Squeeze out the excess mortar at the head joint and at the sides (figure 8-40). Make sure the mortar completely fills the head joint. After bedding the brick, cut off the excess mortar and use it to start the next end joint. Throw any surplus mortar back on the mortar board where it can be restored to workability.
Figure 8-41 shows how to insert a brick into a space left in a wall. First, spread a thick bed of mortar (view 1), and then shove the brick into the wall space (view 2) until mortar squeezes out of all four joints (view 3). This way, you know that the joints are full of mortar at every point.
Figure 8-41.-Inserting a brick in a wall space.
To make a cross joint in a header course, spread the bed joint mortar several brick widths in advance. Then, spread mortar over the face of the header brick before placing it in the wall (figure 8-42, view 1). Next, shove the brick into place, squeezing out mortar at the top of the joint. Finally, cut off the excess mortar as shown in view 2.
Figure 8-42.-Making a cross joint in a header course.
Figure 8-43 shows how to lay a closure brick in a header course. First, spread about 1 inch of mortar on the sides of the brick already in place (view 1), as well as on both sides of the closure brick (view 2). Then, lay the closure brick carefully into position without disturbing the brick already laid (view 3). If you do disturb any adjacent brick, cracks will form between the brick and mortar, allowing moisture to penetrate the wall. You should place a closure brick for a stretcher course (figure 8-44) using the same techniques as for a header course.
As we mentioned earlier, filling exposed joints with mortar immediately after laying a wall is called pointing. You can also fill holes and correct defective mortar joints by pointing, using a pointing trowel.
To cut a brick to an exact line, you should use a chisel (figure 8-45), or brick set. The straight side of the tools cutting edge should face both the part of the brick to be saved and the bricklayer. One masons hammer blow should break the brick. For extremely hard brick, first roughly cut it using the brick hammer head, but leave enough brick to cut accurately with the brick set.
Figure 8-45.-Cutting brick with a chisel.
Use a brick hammer for normal cutting work, such as making the closure bricks and bats around wall openings or completing corners. Hold the brick firmly while cutting it. First, cut a line all the way around the brick using light hammer head blows. Then, a sharp blow to one side of the cutting line should split the brick at the cutting line (figure 8-46, view 1). Trim rough spots using the hammer blade, as shown in view 2.
Figure 8-46.-Cutting brick with a hammer.
The exterior surfaces of mortar joints are finished to make brick masonry waterproof and give it a better appearance. If joints are simply cut to the face of the brick and not finished, shallow cracks will develop immediately between the brick and the mortar. Always finish a mortar joint before the mortar hardens too much. Figure 8-47 shows several types of joint finishes, the more important of which are concave, flush, and weather.
Figure 8-47.-Joint finishes.
Of all joints, the concave is the most weather tight. After removing the excess mortar with a trowel, make this joint using a jointer that is slightly larger than the joint. Use force against the tool to press the mortar tight against the brick on both sides of the mortar joint.
The flush joint is made by holding the trowel almost parallel to the face of the wall while drawing its point along the joint.
A weather joint sheds water from a wall surface more easily. To make it, simply push downward on the mortar with the top edge of the trowel.
A well-constructed brick arch can support a heavy load, mainly due to the way weight is distributed over its curved shape. Figure 8-48 shows two common arch shapes: elliptical and circular. Brick arches require full mortar joints. The joint width is narrower at the bottom of the arch than at its top, but it should not narrow to less than 1/4 inch at any point. As laying progresses, make sure the arch does not bulge out of position.
Figure 8-48.-Common arch shapes.
It is obviously impossible to construct an arch without support from underneath. These temporary wooden supports must not only be able to support the masonry during construction but also provide the geometry necessary for the proper construction and appearance of the arch. Such supports are called templets.
Figure 8-49.-Using a template to construct an arch.
Lay out the arch carefully so that you dont have to cut any bricks. Use an odd number of bricks so that the key, or middle, brick falls into place at the exact arch center, or crown. The key, or middle, brick is the last one laid. To determine how many bricks an arch requires, lay the templet on its side on level ground and set a trial number of bricks around the curve. Adjust the number of bricks and the joint spacing (not less than 1/4-inch) until the key brick is at the exact center of the curve. Then, mark the positions of the bricks on the templet and use them as a guide when laying the brick.
|David L. Heiserman, Editor||
Copyright © SweetHaven
Revised: June 06, 2015