Drywall (Gypsum) Board

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.