Introduction
Drywall, a larger gypsum board, was developed at the conclusion of World War II to replace
plaster on rock lath. The
larger board reduced the installation time. In addition, it was
discovered that the full layers of plaster used to cover the rock lath and
seam could be replaced with taping and plastering only the seams. In
addition to being used as the original wall finish, drywall can be used to
cover deteriorated or cracked plaster walls and ceilings.
Installation
Drywall, usually 4 feet wide and 8 feet long (but as long as
16 feet), is nailed or screwed to the structure. The seams are then
"taped" to make the surface smooth and prevent the seams from
cracking Taping typically involves 3 coats of joint compound.
- The first coat secures the tape (paper, plastic mesh or fiberglass
mesh) to the wall. Joint
compound is applied and the tape is placed on the wet compound. The
tape is pressed into compound and the surface is wiped smooth with a 6-inch,
flexible
taping knife. To make the first coat process easier, a tape gun that puts the joint compound and tape on the wall
at the same time can be used.
- The second coat of joint compound is applied over the joint and
smoothed with a wider (10 to 12-inch) trowel, to blend the seam and tape
into the wall surface.
- A finish coat, like the second coat, is applied with a wider 16-inch
trowel to blend the seam into the wall surface even more. Light sanding
may be needed after each coat to remove any ridges of compound.
Types of Drywall Board
There are three types of drywall/gypsum board:
- Fire-rated or type "X" drywall are fire-resistant. They are a minimum of 5/8 inches
thick and are installed generally in the same way as standard gypsum board.
An “X” is stamped on the board to indicate the material is fire-rated. Fire-rated drywall is most often used to finish the common
(or party) walls between condominiums or townhouses. In some
locations, building codes require
fire-rated
gypsum board on the walls and ceilings between the living space and an attached garage.
- Standard gypsum is a 4-foot by 8 to16-foot board that is usually a
1/2-inch (but also comes in 1/4-inch or 5/8-inch) thick
sheet.
- Water-resistant (not waterproof) gypsum board is essentially standard
drywall, except the paper skin (green or brown in color) is treated with
a small amount of asphalt and is used in locations with high moisture,
such as in the bathroom and kitchen. It is installed in the same
manner as the other gypsum board products. The life expectancy of ceramic tile on walls with
green-board or water-resistant drywall substrate is approximately 12 to 16
years in a bathtub/shower area, and 9 to 12 years in a shower area. Ceramic tile on wet bed (plaster) or other waterproof substrates,
such as Wonder-Board, may last decades longer.
Common Defects
The most common defects in gypsum board are nail pops, tape coming loose
at corners and tears in the seams. Nail pops are common, and to some extent,
should be expected. Structural adhesives and screws have improved this
situation over the years.
Nail pops indicate the nail is no longer secure. To ensure the nail
does not pop out again, repair by placing a screw or nail into the joist or
stud, one inch from and on both sides of the nail and refinish the
surface.
Truss Roof Framing Systems and Drywall Nail Pops
Nail pops from “truss
lift” may reoccur every winter when the truss system expands and
contracts. The cause of truss lift is not known, but it is assumed
that a combination of temperature and humidity changes that accompany the
change of seasons cause the upper portion of the truss to cool and dry more
than the bottom cord to which the drywall is secured. The cooler and
drier part will contract and pull the warmer and moister bottom cord (under
insulation and close to the heated living area) away from the drywall
ceiling. There is no solution to this, but in
some cases, a small crown molding can be installed (nailed to the ceiling
only) to cover the affected area during the seasonal movement. Nail pops
are most evident along the
center-bearing wall of the house.
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