SECTION II. CONSTRUCTION PROCEDURES
MODULAR COORDINATION AND PLANNING
8-13. Modular coordination is when the design of a building, its components, and the building-material units all conform to a dimensional standard based on a modular system. Modular measure is the system of dimensional standards for buildings and building components that permit field assembly without cutting. The basic unit is a 4-inch cube that allows a building to be laid around a continuous three-dimensional rectangular grid having 4-inch spacing. The modular system of coordinated drawings is based on a standard 4-inch grid placed on the width, length, and height of a building, as shown in Figure 8-2.
Figure 8-2. Elements of modular design
Step 1. Use the grid on preprinted drawing paper for both small-scale plans and large-scale details. Do not use drawing paper with a scale less than 3/4 inch which equals 1 foot to show grid lines at 4-inch spacing.
Step 2. Select a larger planning module that is a multiple of 4 inches. For floor plans and elevations, for example, the module may be 2 feet 8 inches, 4 feet, 5 feet, 6 feet 4 inches, and so forth.
Step 3. Show materials actual size, or to scale, and locate them on or related to a grid line by reference dimensions. Dimensions falling on grid lines are shown by arrows; those not falling on grid lines, by dots (see Figure 8-2 above).
Maintain constant awareness of standard modular dimensions in planning, and preplan the work to make use of as many standard- sized building materials as possible. Such planning saves considerable labor, time, and materials.
Make maximum use of full- and half-length units when laying out concrete masonry walls to minimize cutting and fitting units on the job.
Plan the wall length and height, the width and height of openings, and wall areas between doors, windows, and corners to use full- and half-size units as shown in Figure 8-3. Remember that window and door frames must have modular dimensions to fit modular full- and half-size masonry units.
Keep all horizontal dimensions in multiples of nominal full-length masonry units. Both horizontal and vertical dimensions should be designed in multiples of 8 inches. Table 8-1 below gives the nominal lengths of modular-concrete masonry walls in the number of stretchers, and Table 8-2 below gives the nominal heights of modular-concrete masonry walls in the number of courses.
Plan the horizontal dimensions in multiples of 8 inches (half-length units) and the vertical dimensions in multiples of 4 inches, when using 8 by 4 by 16 blocks. If the wall thickness is either greater or less than the length of one half-length unit, use a special length unit at each corner in each course.
Figure 8-3. Planning concrete masonry wall openings
Table 8-1. Nominal length of modular-concrete masonry walls in stretchers
Table 8-2. Nominal height of modular-concrete masonry walls in courses
WALLS AND WALL FOOTINGS
8-14. Place masonry wall footings on firm, undisturbed soil having adequate load-bearing capacity to carry the design load and below frost penetration. Unless local requirements or codes specify otherwise, make the footings for small buildings twice as wide as the thickness of the walls they support. Table 8-3 below gives both the unit weights and quantities for modular-concrete masonry walls. Footing thickness equals wall width (see Figure 8-4 below).
Table 8-3. Unit weight and quantities for modular concrete masonry walls
Figure 8-4. Dimensions of masonry wall footings
8-15. If you expect the groundwater level during a wet season to reach the basement floor elevation, place a line of drain tile along the exterior side of the footings. The tile line should fall at least 1/2 inch in 12 feet and drain to a suitable outlet. Place pieces of roofing felt over the joints to keep out sediment during backfilling. Cover the tile line to a depth of 12 inches with a permeable fill of coarse gravel or crushed stone ranging from 1 to 1 1/2 inches in size. When the first floor is in place, fill the balance of the trench with earth from the excavation.
8-16. Always give exterior concrete masonry basement walls two 1/4-inch thick coats of parging, using either portland cement mortar (1:2 1/2 mix by volume) or joint mortar.
Step 1. In hot, dry weather dampen the wall surface very lightly with a fog water spray before applying the first parging coat.
Step 2. Roughen the first coat when it is partly hardens, to provide a bond for the second parging coat.
Step 3. Wait for the first coat to harden for 24 hours, then dampen it lightly just before applying the second coat. Keep the second coat damp for at least 48 hours following application.
Step 4. For below-grade parged surfaces in very wet soils, use two continuous coatings of bituminous mastic brushed over a suitable priming coat. Make sure that the parging is dry before you apply the primer and that the primer is dry when you apply the bituminous mastic. Do not backfill against concrete masonry walls until the first floor is in place.
FLOOR AND ROOF SUPPORT
8-17. Use solid masonry courses to support floor beams or floor slabs to help distribute the loads over the walls as well as provide a termite barrier. Use either solid masonry units or fill the cores of hollow block with concrete or mortar. If using blocks that are filled with mortar, lay strips of expanded metal lath in the bed joint underneath to support the fill.
WEATHERTIGHT CONCRETE MASONRY WALLS
8-18. Good workmanship is a very important factor in building weathertight walls.
Step 1. Lay each masonry unit plumb and true.
Step 2. Fill both horizontal and vertical joints completely; compact them by tooling when the mortar partly stiffens.
Step 3. Add flashing at vertical joints in copings and caps, at the joints between the roofs and walls, and below cornices and other members that project beyond the wall face.
Step 4. Shed water away from the wall surface by providing drips for chimney caps, sills, and other projecting ledges. Make sure that drains and gutters are large enough so that overflowing water does not run down masonry surfaces.
8-19. The first step in building a concrete masonry wall is to locate the corners of the structure. Then check the layout by placing the first course blocks without mortar (see Figure 8-5).
Figure 8-5. Laying first course of blocks for a wall
Step 1. Use a chalked snapline to mark the footing and align the blocks accurately.
Step 2. Replace the loose blocks with a full bed of mortar, spreading and furrowing it with a trowel to ensure plenty of mortar under the bottom edges of the first course.
Step 3. Use care to position and align the corner block first.
Step 4. Lay the remaining first course blocks with the thicker end up to provide a larger mortar-bedding area.
Step 5. Apply mortar to the block ends for the vertical joints by placing several blocks on end and buttering them all in one operation. Make the joints 3/8 inch thick.
Step 6. Place each block in its final position and push it down vertically into the mortar bed and against the previously laid block to obtain a well-filled vertical mortar joint.
Step 7. Use a mason's level after laying three or four blocks as a straightedge to check correct block alignment (see Figure 8-6).
Figure 8-6. Leveling and plumbing first course of blocks for a wall
Step 8. Use the level to bring the blocks to proper grade and make them plumb by tapping with a trowel handle as shown in Figure 8-6.
Step 9. Lay out the first course of concrete masonry very carefully, making sure that it is properly aligned, level, and plumb. This ensures that succeeding courses and the final wall are both straight and true.
LAYING UP THE CORNERS
8-20. After laying the first course, build up the corners of the wall next, usually four or five courses high.
Step 1. Move back each course one-half block.
Step 2. Apply mortar only to the tops of the blocks of the horizontal joints already laid.
Step 3. Apply mortar to the vertical joints either to the ends of the new block or the end of the block previously laid, or both, to ensure well-filled joints (see Figure 8-7).
Figure 8-7. Vertical joints
Step 4. Lay each course at the corner, check it with a level for alignment for leveling and for ensuring that it is plumb (see Figure 8-8).
Figure 8-8. Checking each course at the corner
Step 5. Use care to check each block with a level or straightedge to make sure that all the block faces are in the same plane to ensure true, straight walls. A story or course pole, which is a board with markings 8 inch apart as shown in Figure 8-9 helps to accurately determine the top of each masonry course.
Figure 8-9. Using a story or course pole
Step 6. Check the horizontal block spacing by placing a level diagonally across the corners of the blocks as shown in Figure 8-10.
Figure 8-10. Checking horizontal block spacing
LAYING BLOCKS BETWEEN CORNERS
8-21. When filling in the wall between the corners, follow the procedures below.
Step 1. Stretch a mason's line along the exterior block edges from corner to corner for each course.
Step 2. Lay the top outside edge of each new block to this line (see Figure 8-11 below). How you grip a block before laying it is important.
First, tip it slightly toward you so that you can see the edge of the course below.
Place the lower edge of the new block directly on the edges of the blocks comprising the course below, as shown in Figure 8-11.
Next, make all final position adjustments while the mortar is soft and plastic, because any adjustments you make after the mortar stiffens will break the mortar bond and allow water to penetrate.
Finally, level each block and align it to the mason's line by tapping it lightly with a trowel handle.
Figure 8-11. Filling in the wall between corners
8-22. Before installing the closure block, butter both edges of the opening and all four vertical edges of the closure block with mortar. Then lower the closure block carefully into place as shown in Figure 8-12. If any mortar falls out leaving an open joint, remove the block and repeat the procedure.
Figure 8-12. Installing a closure block
8-23. To ensure a good bond, do not spread mortar too far ahead of actually laying blocks or it will stiffen and lose its plasticity. The recommended width of mortar joints for concrete masonry units is approximately 3/8 inch thick which--when properly made--helps to produce a weathertight, neat, and durable concrete masonry wall. As you lay each block, cut off excess mortar extruding from the joints using a trowel (see Figure 8-13) and throw it back on the mortar board to rework into the fresh mortar. Do not, however, rework any dead mortar from the scaffold or floor.
Figure 8-13. Cutting off excess mortar from the joints
8-24. Weathertight joints and the neat appearance of concrete masonry walls depend on proper tooling. After laying a section of the wall, tool the mortar joints when the mortar becomes thumbprint hard. Tooling compacts the mortar and forces it tightly against the masonry on each side of the joint. Use either concave or V-shaped tooling on all joints (see Figure 8-14). Tool vertical joints first, followed by striking the horizontal joints with a long jointer (see Figure 8-15 below). Trim off mortar burrs from the tooling flush with the wall face using a trowel or soft bristle brush, or by rubbing with a burlap bag.
Figure 8-14. Tooling mortar joints for weathertight exterior walls
Figure 8-15. Tooling mortar joints
8-25. You must prepare in advance for installing wood plates on top of hollow concrete masonry walls with anchor bolts. To do this, place pieces of metal lath in the second horizontal mortar joint from the top of the wall under the cores that will contain the bolts. Use anchor bolts 1/2 inch in diameter and 18 inches long, spacing them up to a maximum of 4 feet apart. When you complete the top course, insert the bolts into the cores of the top two courses, and fill the cores with concrete or mortar. The metal lath underneath holds the concrete or mortar filling in place. The threaded end of the bolt should extend above the top of the wall as shown in Figure 8-16.
Figure 8-16. Installing anchor bolts for wood plates
8-26. Control joints are continuous vertical joints that permit the masonry wall to move slightly under unusual stresses without cracking. A combination of full- and half-length blocks form the continuous vertical joint as shown in view 1 of Figure 8-17. Lay up control joints in mortar just as any other joint, but if they are exposed to either the weather or to view, caulk them as well. After the mortar is quite stiff, rake it out to a depth of about 3/4 inch to make a recess for the caulking compound as shown in view 2 of Figure 8-17.
Figure 8-17. Making a control joint
Use a thin, flat caulking trowel to force the compound into the joint. You can make a second type of control joint by inserting building paper or roofing felt into the block end cores extending the full height of the joint (see Figure 8-18). Cut the paper or felt to convenient lengths, but wide enough to extend across the joint. The paper or felt material prevents the mortar from bonding on that side of the joint. Use control joint blocks, if available (see Figure 8-18).
Figure 8-18. Control joints made using roofing felt or control joint blocksVertical joints
8-27. The two types of intersecting walls are bearing and nonbearing.
8-28. Do not join intersecting concrete block-bearing walls with a masonry bond, except at the corners. Instead, terminate one wall at the face of the second wall with a control joint. Tie the intersecting walls together with Z-shaped metal-tie bars 1/4 by 1 1/4 by 28 inches in size, having a 2-inch right angle bend on each end (see Figure 8-19). Space the tie bars no more than 4 feet apart vertically, and place pieces of metal lath under the block cores that will contain the tie-bar ends (see Figure 8-16). Embed the right angle bends in the cores by filling them with mortar or concrete (see Figure 8-19)
Figure 8-19. Tying intersecting bearing walls
8-29. To join intersecting nonbearing block walls, terminate one wall at the face of the second with a control joint. Place strips of metal lath or 1/4-inch mesh galvanized hardware cloth across the joint between the two walls in alternate courses. Insert one half of the metal strips into one wall as you build it; tie the other halves into mortar joints as you lay the second wall (see Figure 8-20).
Figure 8-20. Tying intersecting nonbearing walls
8-30. Modular door and window openings usually require lintels to support the blocks over the openings. Use precast concrete lintels that contain an offset on the underside to fit the modular openings or use steel-lintel angles that you install with an offset on the underside (see Figure 8-21) to fit modular openings. In either case, place a noncorroding metal plate under the lintel ends at the control joints to allow the lintel to slip and the control joints to function properly. Apply a full bed of mortar over the metal plate to uniformly distribute the lintel load.
Figure 8-21. Installing precast concrete lintels without and with steel angles
8-31. Install precast concrete sills following wall construction (see Figure 8-22). Fill the joints tightly at the ends of the sills with mortar or a caulking compound.
Figure 8-22. Installing precast concrete sills
PATCHING AND CLEANING BLOCK WALLS
8-32. When laying concrete masonry walls, be very careful not to smear mortar into the block surfaces, because you cannot remove hardened, embedded mortar smears, even with an acid wash; also paint will not cover them. Allow any droppings to dry and harden. You can then chip off most of the mortar with a small piece of broken concrete block (see Figure 8-23), or with a trowel. A final brushing of the spot will remove practically all of the mortar. Always patch mortar joints and fill holes made by nails or line pins with fresh mortar.
Figure 8-23. Cleaning mortardroppings from concrete block wall
8-33. The mason is responsible for laying out the job to do the work properly. Masons must make sure that the walls are plumb and that courses are level. They are also responsible for the quality of all the detail work such as cutting and fitting masonry units, making joints, and installing anchor bolts and ties in intersecting walls.
8-34. The mason's helper mixes mortar, keeps it tempered, and supplies concrete blocks and mortar to the mason as needed. Helpers aid the mason in laying out the job and sometimes lay out blocks ahead on an adjacent course to expedite the mason's work.
|David L. Heiserman, Editor||
Copyright © SweetHaven
Revised: June 06, 2015