Association of Home Appliance Manufacturers
Wallboard and Cement Board
Wallboard

Wallboard is available in thicknesses of 1/4-in.. 3/8-in., 1/2-in. and 5/8-inch. This thickness range may at first glance seem limiting, because greater wall thickness (mass) is needed to achieve better soundproofing or fireproofing in a wall or ceiling. However, you can apply several layers of wallboard to achieve any wall thickness you want, for whatever purpose. For example, two layers of 3/8-inch thick wallboard are often laminated together and used to match the 3/4-inch th.kness of older plaster walls. This technique is often used by remodelers to fill in holes or voids in plaster, and bring the new area into alignment to match the old plaster wall. Also, this wall thickness has both better soundproofing and fireproofing qualities. For example, if you are building a duplex, applying two layers of 3/8-inc. thick wallboard on both sides of the common wall (wall between two living units) will help prevent sound transfer between the two units, and will also prevent any fire from traveling through the common wall and consuming both units.

Why offer so many different thicknesses of wallboard? Keep in mind that, each time you increase the thickness of a wallboard panel by even 1/8-in., that 1/8-in. is solid plaster, so you gain a great deal of strength and stiffness in the panel with each 1/8-in. increase in thickness. The following points explain the need and uses for each thickness of wallboard:

Wallboard Thicknesses

- 1/4in.: Not a stock item at most lumber yards and home centers, 1/4 in. wallboard is used as a new skin for old walls. 1/4 in. wallboard can be adhesive-laminated over old plaster to give it a "new skin," an unbroken new decorating surface. Your supplier will have to special-order 1/4 in. wallboard for you.

- 3/8 in.: This is also a remodeling grade of wallboard. It is not strong enough to be used as a single layer wall finish, although you may find some post-World War II houses, built before the code standards were changed, that have only 3/8 in. thick wallboard on walls and/or ceilings. This thickness can be used as a first layer or underlayment base for applying paneling, or can be adhesive-applied in two layers to get a laminated wallboard finish. Laminated wallboard is considered the best of all walls, because it can be built in a short time and provides the soundproofing and fireproofing qualities of the thicker plaster walls, but is virtually crack-proof if it is properly applied. To have a laminated wallboard job, the first layer of wallboard is nailed or screwed to the walls and ceilings, with the base wallboard parallel to the framing joists or studs. The second layer of wallboard is then adhesive-laminated (glued) over the first layer, but the second layer is applied so the panels are perpendicular to the framing. By applying one layer of wallboard parallel to the framing, the second layer perpendicular to the framing, you ensure that the joints are staggered so they do not occur at the same point on the wall or ceiling.

- 1/2 in.: Because the thinner 3/8 in. wallboard sagged between studs or joists, 1/2 in. thick wallboard quickly became the standard of the industry in postwar housing. This wallboard can be used in single-layer applications for a finished wall or ceiling. Caution: Because roof trusses are now set 24 in. on center (o.c.) rather than 16 in. o.c. as were the ceiling joists in stick framing, and because heavier thicknesses of insulation are now installed on top of wallboard ceilings, 5/8 in.-thick wallboard is now advised for these ceiling applications, to eliminate wallboard sagging between ceiling joists. The wider spacing and the heavier insulation loads must have a stiffer wallboard panel to avoid sagging.

- 5/8: Wallboard starts to get pretty heavy when it is 5/8 in. thick, so this is the thickest wallboard you can buy. For greater thicknesses you must apply multiple layers of wallboard. As mentioned above, you should apply 5/8 in. thick wallboard on ceilings where joist or truss spacing is 24 in. o.c. or greater. 5/8 in. thick wallboard is also specified for firewalls. The wallboard, commonly referred to as "5/8 in.Firecode" must be used on the common wall between a house and an attached garage, and on the garage ceiling. The reason for this requirement is that 1/2 in. thick wallboard has a fire rating of 45 minutes, which means that if burning house temperatures are applied to one side of a wall with 1/2 in. wallboard, the framing inside the wall will start to char or combust after 45 minutes. 5/8 in. Firecode wallboard has a full 60-minute fire rating, which means that framing covered with the 5/8 in. Firecode will combust after 60 minutes. This means that the homeowner gains 15 precious minutes in which to detect and report any fire.

In addition to a variety of thicknesses, wallboard is made in different lengths for special applications. The most common length in home centers is 8 ft., although using 12-ft. long wallboard will give you a much better job, with fewer seams to finish and with greater strength. Although many texts show wallboard being applied parallel to the framing, i.e., 8-ft. long panels "stood up" on the walls, all manufacturers and the Gypsum Association recommend that the best job is obtained when you install 12-ft. long panels perpendicular to the framing. This results in fewer joints to treat, a stronger wall (ties together the maximum number of studs or joists) and joints that are easier to hide. "Joint banding," a defect in which paint over joints appears to be darker or "shadowed" is emphasized when wallboard is applied parallel to the framing. Another argument: standing wallboard up, or installing it parallel to the studs, invariably results in having joints above or at the top corners of doors or windows. This results in cracks, and in joints treated at the corners where you will have difficulty, in trying to fit mitered trim. Use the longest wallboard panels you can handle and apply them perpendicular to the framing. If this seems too difficult it is much better to hire professionals to install the wallboard properly than to do it yourself and end up with the inferior results from applying the wallboard parallel to the framing.

Tips for Installing Wallboard

- Use wallboard adhesives where possible, augmented by wallboard screws positioned as directed by the adhesive manufacturer. Wallboard nails are the very worst choice for installing wallboard, because the repeated blows of the hammer often damage the face of the wallboard panel, and because nails are more prone to "pop." Do not use nails.

- Where there is a vapor barrier that prevents using wallboard adhesives, such as on exterior walls and on the ceiling next to the attic, use a screw gun to drive wallboard screws. Screw length is important to prevent pops: use only 1 in. screws to install 1/2 in. wallboard, and 1-1/4 in. screws to install 5/8 in. thick wallboard. Nails or screws that are too long cause pops or "fastener failures," because the fasteners pop when the wood framing shrinks.

- Inspect wallboard panels before you buy them and after delivery. Wallboard panels often are cracked, or the corners of the panels damaged, during delivery. Do not accept or try to finish or repair damaged wallboard. It is difficult enough to get a good job finishing wallboard when the panels are not damaged: don't make the job more difficult by trying to finish cracked or damaged panels.

Cement Board

Once upon a time all ceramic tile was set on a base of solid concrete. Walls to be tiled were covered with wire lath, then plastered with a full 1 in. layer of concrete. Then came tile adhesives and wallboard construction, and we tried to glue the tile directly to wallboard. The trouble was, we neglected maintaining the grout between the tile, and water penetrated between the tile joints and destroyed the wallboard base, which of course meant that the tile fell on the floor. End of expensive tile job. Enter cement board, known by its trade name of Durock(TM). Cement board is made of cement and fiberglass fibers, and is used as an underlayment for ceramic tile. Cement board will not wick up water and does not fall apart when it is wet. It is easy to cut and nail, and is the best substrate for use in tub or shower areas where you will have ceramic tile. It can also be used for floors or as a ceramic tile base on cabinet countertops, and an exterior cement board can be used as a base for applying stucco.

Written by Gary Branson
Reprinted with permission. Copyright HouseNet, Inc.

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