The types of gypsumboard generally available include wallboard, backing board, coreboard, fire-resistant gypsumboard, water-resistant gypsumboard, gypsum sheathing, and gypsum formboard. Gypsum Wallboard. This type is used for the surface layer on interior walls and ceilings. Regular gypsum wallboard comes with gray liner paper on the back and a special paper covering, usually cream-colored, on facing side and edges. This covering provides a smooth surface suitable for decoration. Foil-backed gypsum wallboard has aluminum foil bonded to the liner paper to serve as a vapor barrier and, when contiguous to an airspace, as thermal insulation. Predecorated gypsum wallboard does not require decorative treatment after installation because it comes with a finished surface, often a decorative vinyl or paper sheet. Wallboard should conform with ASTM C36. Wallboard usually is available 4 ft wide in the following thicknesses and lengths: 1/4 infor covering and rehabilitating old walls and ceilings, 4 to 12 ft long 5/16 inwhere thickness greater than 1/4 in is desired, 4 to 14 ft long. 3/8 inmainly for the outer face in two-layer wall systems, 4 to 16 ft long 1/2 infor single-layer new construction with supports 16 to 24 in c to c, 4 to

In the training workshop we are most likely to use a steel square to set out our brickwork. Care and accuracy are once again the main requirements. Having set out and laid our first course as already described, we place one leg of the steel square against the face of the first course to create an accurate angle for our return to follow. After we have laid our return bricks we need to ensure that they are level. Always level from the corner point to the end of the course you are laying. This applies to each course we lay as we build our quoin to the intended height. Laying and levelling from the corner point maintains accuracy. If we keep in mind the sequence already mentioned for building a brick rack, we can speed up our work rate and add to our efficiency. Remember: gauge level plumb line. Lets review some techniques that help us maintain quality and standards. Keep in mind that the spirit level is a precision instrument. Never strike the spirit level to align bricks horizontally.

c  68.1  (5.263) where E  modulus of elasticity, psi p  density of the struck body, lb/ ft3 If an impact imparts a velocity v, ft / s, to the particles at one end of a prismatic bar, the stress, psi, at that end is v  E  0.0147v Ep  0.000216pcv (5.264) c if is in the elastic range. In a compression wave, the velocity of the particles is in the direction of the wave. In a tension wave, the velocity of the particles is in the direction opposite the wave. In the plastic range, Eqs. (6.263) and (5.264) hold, but with E as the tangent modulus of elasticity. Hence, c is not a constant and the shape of the stress wave changes as it moves. The elastic portion of the stress wave moves faster than the wave in the plastic range. Where they overlap, the stress and irrecoverable strain are constant. (The impact theory is based on an assumption difficult to realize in practice that contact takes place simultaneously over the entire end of the bar.) At the free end of a bar, a compressive stress wave is reflected as an equal tension wave, and a tension wave as an equal compression wave. The velocity of the particles there equals 2v. At a fixed end of a bar, a stress wave is reflected unchanged. The velocity of the particles there is zero, but the stress is doubled, because of the superposition of the two equal stresses on reflection. For a bar with a fixed end struck at the other end by a moving mass weighing Wm lb, the initial compressive stress, psi, is  0.0147v Ep (5.265) o o where vo is the initial velocity of the particles, ft / s, at the impacted end of the bar and E and p, the modulus of elasticity, psi, and density, lb/ ft3, of the bar. As the velocity of Wm decreases, so does the pressure on the bar. Hence, decreasing compressive stresses follow the wave front. At any time t  2L/c, where L is the length of the bar, in, the stress at the struck end is  e2t /  (5.266) o where e  2.71828,  is the ratio of Wb, the weight of the bar, to Wm, and