Joint tape, a strip of strong paper reinforcement with feathered edges, for embedment in joint compound. Sometimes supplied with small perforations, the tape usually is about 2 in wide and 1/16 in thick. Joint compound, and adhesive, with or without fillers, for bonding and embedding the tape. Two types may be used. One, usually referred to as joint, or taping, compound, is applied as an initial coat for filling depressions at joints and fasteners and for adhering joint tape. The second, called topping, or finishing, compound, is used to conceal the tape and for final smoothing and leveling at joints and fasteners. As an alternative, an all-purpose compound that combines the features of taping and topping compounds may be used for all coats. Compounds may be supplied premixed, or may require addition of water on the job. Flush Joints and Fasteners. For concealing fastener heads and where wallboards in the same plane meet, at least three coats of joint compound should be used. The first coat, of taping compound, should be used for adhering tape at edges and ends of the boards and to fill all depressions over fastener heads and at tapered edges. Joint tape should be centered over each joint for the length or width of the wall or panel and pressed into the compound, without wrinkling, with a tape applicator, a broad knife. Excess compound should be redistributed as a skim coat over the tape. A skim coat of joint compound applied immediately after tape embedment reduces the possibility of edge wrinkling or curling, which may result in edge cracking. A second, or bedding, coat should be applied with topping compound at fastener heads and joints after the taping compound has dried. The waiting period may be 24 hr if regular taping compound is used, and about 3 hr if a quick-setting compound is used. This bedding coat should be thin. At joints, it should completely cover the tape and should be feathered out 1 to 2 in beyond each edge of the tape at tapered edges, and over a width of 10 to 12 in at square edges. When the coat has dried, a second, thin coat of the topping compound should be applied for finish at fasteners and joints. At joints, it should completely cover the preceding coat and should be feathered out 1 to 2 in beyond its edges at tapered edges, and over a width of 18 in at square edges. Irregularities may be removed by light sanding after each coat has hardened. But if joint treatment is done skillfully, such sanding should not be necessary. Reentrant Corners. Treatment of interior corners differs only slightly from that of flush joints. Joint compound should first be applied to both sides of each joint. Joint tape should be creased along its center, then embedded in the compound to form a sharp angle. After the compound has dried, finishing compound should be applied, as for flush joints. Trim. Exposed corners and edges should be protected with a hard material. Wood or metal casings may be used for protection and to conceal the joints at door and window frames. Baseboard may be attached to protect wallboard edges at floors. Corner beads may be applied at exterior corners when inconspicuous protection is desired. Casing beads may be similarly used in other places. At least three-coat finishing with joint compound is required to conceal fasteners and obtain a smooth surface with trim shapes. Decoration. Before wallboard is decorated, imperfections should be repaired. This may require filling with joint compound and sanding. Joint compound should be thoroughly dry before decoration starts. FIGURE 11.27 Control joints: (a) expansion joint in a plastered, metal-stud partition: (b) control joint in a wallboard, metal-stud wall; (c) control joint in a plastered, suspended ceiling. The first step should be to seal or prime the wallboard surface. (Glue size, shellac, and varnish are not suitable sealers or primers.) An emulsion sealer blocks the pores and reduces suction and temperature differences between paper and joint compound. If wallpaper is used over such a sealer, the paper can be removed later without damaging the wallboard surface and will leave a base suitable for redecorating. A good primer provides a base for paint and conceals color and surface variations. Some paints, such as high-quality latex paints, often have good sealing and priming properties. Plaster and gypsumboard construction have low resistance to stresses induced by structural movements. They also are subject to dimensional changes because of changes in temperature and humidity. If proper provision is not made in the application of plaster and gypsumboard systems for these conditions, cracking or chipping may occur or fasteners may pop out. Generally, such defects may be prevented by applying these systems so that movement is not restrained. Thus, gypsumboard or lath and plaster surfaces should be isolated by expansion or control joints, floating angles, or other means where a partition or ceiling abuts any structural element, except the floor, or meets a dissimilar wall or partition assembly, or other vertical penetration. Isolation also is advisable where the construction changes in the plane of the partition or ceiling. In addition, expansion or control joints should be inserted where expansion or FIGURE 11.28 Floating interior angles with gypsumboard construction (gypsum lath similar): (a) omission of nails at intersections; (b) wall-ceiling intersection with ceiling boards applied parallel to joists; (c) wall-ceiling intersection with ceiling boards applied perpendicular to joists; (d ) reentrant

N
(10.32) P sin2   Q cos2  where N, P, and Q are, respectively, the adjusted design value, lb, or stress, psi, at inclination  with the direction of grain, parallel to grain, and perpendicular to grain. Design values are based on the assumption that the wood at the joint is clear and relatively free from checks, shakes, and splits. If knots are present in the longitudinal projection of the net section within a distance from the critical section of half the diameter of the connector, the area of the knot should be subtracted from the area of the critical section. It is assumed that slope of the grain at the joint does not exceed 1 in 10. The stress, whether tension or compression, in the net area, the area remaining at the critical section after subtracting the projected area of the connectors and the bolt from the full cross-sectional area of the member, should not exceed the design value of clear wood in compression parallel to the grain. Tables in the NDS list the least thickness of member that should be used with the various sizes of connectors. The design values listed for the greatest thickness of member with each type and size of connector unit are the maximums to be used for all thicker material. Design values for members with thicknesses between those listed may be obtained by interpolation. The NDS also lists minimum end and edge distances and spacing for timber connectors (Table 10.37). Edge distance is the distance from the edge of a member to the center of the connector closest to that edge and measured perpendicular to the edge. End distance is measured parallel to the grain from the center of the connector to the square-cut end of the member. If the end of the member is not cut normal to the longitudinal axis, the end distance, measured parallel to that axis from any point on the center half of the connector diameter that is perpendicular to the axis, should not be less than the minimum end distance required for a squarecut member. Spacing of connectors is measured between their centers along a line

5 When we are satisfied that the laid bricks are level with each other, we can attach a string line (line and pins) to the top face arris at each end. We now have an accurate level reference to lay the rest of the first course to. The following step by steps show the key points in the method for laying out a level first course. STEP 1 Mark the two ends of the wall. STEP 2 Lay a brick on a mortar bed at both ends. STEP 3 Use a straight edge to check the bricks are level. STEP 4 Use the spirit level to confirm a level wall. STEP 5 Attach using a string and line. A bricklayer is not the only tradesperson who uses a straight edge. Think about what other trades might use a straight edge and write down what jobs they would use them for. Think about where an operative would use a straight edge when looking in Our House. Attaching a line to the two isolated bricks can pose problems. A string line needs to be as tight as possible. We dont want it to sag in the middle since our course of brickwork would follow the sag and would look unacceptable. However, if we pull the line too tight, it could dislodge our carefully positioned bricks. Getting the tension right is something that comes with experience. A little later, we will look at attaching our line and pins to the brickwork we build at each end of a wall.