MR (moisture resistant) or WR (water resistant)
board is also called greenboard and blueboard. Being
water resist ant, this board is appropriate for bathrooms,
laundries, and similar areas with high moisture. It also
provides a suitable base for embedding tiles in mastic.
MR or WR board is commonly 1/2 inch thick.
Sound-deadening board is a sublayer used with
other layers of drywall (usually type X); this board is
often 1/4 inch thick
Backing board has a gray paper lining on both sides.
It is used as a base sheet on multilayer applications.
Backing board is not suited for finishing and decorating.
Foil-backed board serves as a vapor barrier on
exterior walls. This board is available in various
Vinyl-surfaced board is available in a variety of
colors. It is attached with special drywall finish nails and
is left exposed with no joint treatment.
Plasterboard or gypsum lath is used for plaster base.
It is available in thickness starting at 3/8 inch, widths 16
and 24 inches, and length is usually 48 inches. Because
it comes in manageable sizes, its widely used as a
plaster base instead of metal or wood lath for both new
construction and renovation. This material is not
compatible with portland cement plaster.
The varying lengths of drywall allow you to lay out
sheets so that the number of seams is kept to a minimum,
End points can be a problem, however, since the ends of
the sheets arent shaped (only the sides are). As sheet
length increases, so does weight, unwieldiness, and the
need for helpers. Standard lengths are 8, 9, 10, 12, and
14 feet. Sixteen-foot lengths are also available. Use the
thickness that is right for the job. One-half-inch drywall
is the dimension most commonly used. That thickness,
which is more than adequate for studs 16 inches on
center (OC), is also considered adequate where studs are
24 inches OC. Where ceiling joists are 16 inches OC,
use 1/2-inch drywall, whether it runs parallel or
perpendicular to joists. Where ceiling joists are 24
inches OC, though, use 1/2-inch drywall only if the
sheets are perpendicular to joists.
Drywall of 1/4- and 3/8-inch thicknesses is used
effectively in renovation to cover existing finish walls
with minor irregularities. Neither is adequate as a single
layer for walls or ceiling, however. Two 1/4-inch-thick
plies are also used to wrap curving walls.
Drywall of 5/8-inch thickness is favored for quality
single-layer walls, especially where studs are 24 inches
OC. Use 5/8-inch drywall for ceiling joists 24 inches
OC, where sheets run parallel to joists. This thickness is
widely used in multiple, fire-resistant combinations.
There are several types of edging in common use.
Tapered allows joint tape to be bedded and built up to a
flat surface. This is the most common edge used.
Tapered round is a variation on the first type. Tapered
round edges allow better joints. These edges are more
easily damaged, however. Square makes an acceptable
exposed edge. Beveled has an edge that, when left
untapped, gives a paneled look.
Commonly used tools in drywall application
include a tape measure, chalk line, level, utility and
drywall knives, straightedge, and a 48-inch T square
(drywall square) or framing square. Other basic tools
include a keyhole saw, drywall hammer (or convex head
hammer), screw gun, drywall trowel, comer trowel, and
a foot lift. Some of these tools are shown in figure 5-2.
The tape measure, chalk line, and level are used for
layout work. The utility and drywall knives,
straightedge, and squares are used for scoring and
breaking drywall. The keyhole saw is used for cutting
irregular shapes and openings, such as outlet box
openings. A convex head or drywall, hammer used for
drywall nails will dimple the material without tearing
the paper. The screw gun quickly sinks drywall screws
to the adjusted depth and then automatically disengages.
Drywall knives have a variety of uses. The 6-inch
knife is used to bed the tape in the first layer of joint
compound and for filling nail or screw dimples. The
12-inch finishing knife feathers out the second layer
of joint compound and is usually adequate for the third
or topping layer. Knives 16 inches and wider are used
for applying the topping coat. Clean and dry drywall
knives after use. Use only the drywall knives for the
purpose intended-to finish drywall.
The drywall trowel resembles a concrete finishing
trowel and is manufactured with a 3/16-inch concave
bow. This trowel, also referred to as a flaring,
feathering, or bow trowel, is used when applying
the finish layer of joint compound. A comer trowel is
almost indispensable for making clean interior comers.
For sanding dried joint compound smooth, use 220
grit sandpaper. Sandpaper should be wrapped around a
sanding block or can be used on an orbital sander. When