Drywall Contracting
Chapter Preview

Introduction | Table of Contents | Back Cover

CHAPTER 1
DRYWALL APPLICATIONS

Gypsum has been used in construction for thousands of years because it's cheap, durable and easy to work with. In the 1940's and 1950's, gypsum drywall replaced plaster as the material of choice for interior wall covering. Before inexpensive, high quality drywall was available, interior walls in most homes were lathed and plastered.
Plaster is still an excellent wall cover. But application takes considerably more labor, specialists must do I the work, it's messy, and it leaves the building saturated with moisture that has to evaporate before painting and finishing can begin. Carpenters can hang gypsum drywall; it costs less, leaves less of a mess, I and requires far less moisture for application. That's how gypsum wallboard got its name, drywall. The wall is covered with a dry material that can be finished shortly after application is complete.
You may know gypsum drywall by other names. For example, some builders call it sheetrock or plasterboard or gypsum wallboard or simply gyp board. All these names refer to drywall. Some names are trademarks. To simplify matters, we'll call the product drywall throughout this book.
If you make your living with drywall, there are some basic principles you should understand. That's the subject of this first chapter. I'll describe how drywall panels are made. Then I'll suggest some advantages you may not have considered in using drywall. We'll discuss common panel sizes and types. Finally, we'll take a brief look at the various panel edge treatments.

From Mineral Deposit to Drywall
Gypsum is found all over the world in natural deposits that can be mined. In its purest form, gypsum is white. But in the earth it can be different shades of gray, brown or even pink, depending on the impurities present. These impurities include clay and iron oxides. Chemically, gypsum is hydrous calcium sulfate.
Here's how the raw mineral is converted into those familiar white panels. Once the mineral is removed from the earth, it's crushed into small particles. These particles are then heated to about 350 degrees Fahrenheit to drive off nearly all the moisture. This turns the gypsum into a dry powder, which is then mixed with additives, aggregates and fibers to add strength and moisture resistance.
Next, water is added to this mixture so it can be molded and shaped into the form needed. For drywall, the moist gypsum is formed between two layers of paper or other covering. As the gypsum mixture dries, crystals form and interlock, gradually turning the board into a rock-hard mass. Before it's hardened completely, the board is cut to length and passed through dryers that remove any free moisture. This is important. Drywall swells when it gets wet and shrinks as it dries. Too much shrinking and swelling will spoil any drywall job.

ADVANTAGES OF DRYWALL CONSTRUCTION

Drywall is cheap compared to other wall materials. But there are other advantages: fire protection, noise insulation and ease of installation.

Superior fire protection: When drywall is exposed to high temperatures, as in a fire, here's what happens. The outer layer of gypsum that's exposed to heat releases water in the form of steam. This has a cooling effect and limits the temperature rise in the drywall. This process is known as calcining. When calcining takes place, the dehydrated gypsum turns back into a powder that's a good insulator. Heat at the surface is kept away from gypsum below the surface.

Noise protection: The relatively high density of gypsum provides better sound damping than lighter wall materials such as plywood or hardboard. The more dense a material is, the greater its sound-absorbing capacity.

Ease of installation: Drywall panels are easy to install. After World War II, some building materials weren't available and there was a shortage of skilled tradesmen. Builders were eager to try materials that were available and could be installed quickly. Drywall became the most popular wall covering material in nearly every community in the U.S.

PANEL SIZES
Drywall Type	Thickness	Width	Length
Standard gypsum drywall panels	1/4"	4'	8',10',12'
	5/16"	4'	8',10', 12'
	3/8"	4'	8',10',12'
	1/2"	4'	8' to 16'
Fire-resistant drywall Type X for commercial use where multiple layers are required for extended fire wall rating durations	1/2"	4'	8' to 16'
Fire-resistant drywall Type X	5/8"	4'	8' to 16'
Fire-resistant backer board Type X	1/2"	4'	8'
	5/8"	4'	8'
Fire-resistant shaft liner drywall	1"	23-7/8"	8' to 12'
Water-resistant drywall	1/2"	4'	8', 10', 12'
Fire- and water-resistant drywall	1/2"	4'	8', 10', 12'
	5/8"	4'	8',10', 12'
Foil-back panels	3/8"	4'	6' to 16"
	1/2"	4'	6' to 16"
Foil-back Type X	5/8"	4'	6' to 16"
54" wide panels	1/2"	54"	8', 10', 12'
	5/8"	54"	8',10' ,12'
Exterior ceiling panels (soffit board)	1/2"	4'	8',9',10'
	5/8"	4'	8',9',1 0'
High strength ceiling panels	1/2"	4'	8',9',10'
Drywall panels for factory decoration	5/16"	4'	cut to specified size
Sound deadening panels	1/4"	4'	8'
Tile backing panels	1/4"	32",4'	4'
	1/2"	4'	5',8'</ td>
Type X fire resistant tile backing panels	5/8"	4'	8'
Exterior sheathing	1/2"	4'	8',9',10'
	5/8"	4'	8',9',1 0'
Veneer-base drywall (blue board)	3/8"	4'	8' to 16"
	1/2"	4'	8' to 16"

PANEL TYPES
Most interior rooms in a house or office building will take standard drywall panels. But some structures have special requirements, such as increased fire resistance, water resistance, exterior applications, backing board, coreboard, formboard, lath, blocking, radiant heating, decorated and veneer-base panels. Let's look at these special panels.

Standard Drywall Panels
Standard drywall panels have a paper covering on each side and on the long edges. The backs of the panels are surfaced with gray liner paper. The facing is a manila paper, which extends over the long edges. The manila facing paper is also light gray. It's smooth and will take a wide variety of finishes.
The long edges are usually tapered, as shown in Figure 1-1. This is a shallow taper about 2-1/2 inches wide. It reduces the edge thickness by only about 1/16 inch. The taper makes it easier to tape and fill the joint between two pieces of drywall. When filled, taped and sanded, the surface at the joint should be as smooth and even as the board itself. It can be finished with smooth or texture surface, or covered with vinyl. Standard drywall is available in the dimensions shown in Table 1. Most dealers stock at least the 8-foot length.
The length of panel you use will depend on the application and panel thickness required. Longer sheets are heavier and harder to handle. They're also more likely to break during handling. You have to be careful with them. But longer sheets can cut down on the number of joints you have to finish. Weigh the advantages of longer sheets with fewer joints against the inconveniences that come with longer panels.
Use standard drywall where there are no special requirements. You can use it in most rooms in a house or office building. Where standard drywall isn't good enough, select the special panel you need. The next few paragraphs describe special applications.

Fire Resistant Panels
Fire-resistant drywall panels are usually marked Type X. Type X panels look like standard drywall panels except that they're stamped "Fire-Resistant" or "Type X" on the back of the panel.
Drywall already has its own built-in fire protection. In Type X panels, adding glass fibers to the core increases the fire resistance. The panels come in both 1/2- and 5/8-inch thicknesses. The 1/2-inch thickness has a fire rating of 45 minutes. The 5/8-inch thickness has a 60-minute fire rating,
Use Type X panels wherever you need high fire resistance. The extra fire protection they offer may let you use thinner drywall. For example, one thickness of Type X may give the same fire rating as multiple layers of standard drywall. To get maximum fire resistance from Type X panels, you have to follow special joint finishing procedures. Otherwise, fire and heat would go around or between the panels. I'll describe the procedure in detail later.
Refer to Table 1 for widths and lengths.

Fire-resistant Shaft Liner Drywall
Use fire-resistant shaft liner drywall in ventilation shafts, stairwells, and separation walls. It has a Type X core, square or tapered edges, and is intended for use with metal studs or in solid gypsum walls. The paper covering is moisture-resistant.

Water-Resistant Panels
Water-resistant drywall panels are also known as WR panels, moisture-resistant (MR), or greenboard. Use these panels in areas that are exposed to high moisture. Kitchens and baths are good candidates for water resistant panels. The facing paper on WR panels is light green. The backing paper is gray or brown.
On WR panels, both the paper covering and the core are water-resistant. The paper is multi-layered and is treated with chemicals that keep moisture out. Asphalt compounds are added to the gypsum core so it won't absorb any moisture, even when there's a tear in the paper.
Apply WR panels directly to the studs without a vapor barrier behind them, Be absolutely sure you install the panels with water-resistant joint compound and finish them according to the manufacturer's recommendations. Refer to Table 1 for widths and lengths.

Fire- and Water-Resistant Panels
Water-resistant panels are also available with a high fire resistance rating. Use these panels in situations where fire separation is required but where the panels may be exposed to high moisture during normal use or during construction. Refer to Table 1 for widths and lengths.

Foil Back Panels
Foil-back drywall is also known as insulating drywall. Foil back drywall is made by laminating aluminum foil to the back surface of drywall panels. The foil creates a waterproof membrane, creating an effective vapor barrier. The reflective surface of the foil adds to the insulating value of the drywall. Foil backing is available on many types of drywall panels for different applications.
You can use foil-back panels with steel or wood framing or furred masonry. But don't use them as a base for tile or other highly moisture-resistant coverings and don't use them in hot, humid climates. If you do, the gypsum core will absorb and trap moisture. Trapped moisture will cause the core to deteriorate, weakening the drywall. Eventually, it will begin to warp, sag or crumble. Refer to Table 1 for widths and lengths.
Foil-back drywall is also available in 5/8" thick Type X for added fire resistance.

54" Wide Panels
Use 54" wide drywall panels for interior walls and ceilings where the added width will eliminate joints. It can be applied to wood or metal framing, and can be formed to curved surfaces. Refer to Table 1 for lengths.

Exterior Ceiling Panels
Use exterior drywall ceiling panels, also called soffit board, on horizontal overhead surfaces, such as soffits, canopies and carport ceilings. These panels are weather-resistant as long as they're not directly exposed to the weather. A water-resistant gypsum core is wrapped with water-repellent beige facing paper suitable for decorating. Finish the joints with battens or joint tape and water-resistant joint compound.
Exterior ceiling panels come 4 feet wide and 8 to 10 feet long. The panels are available in 1/2- and 5/8-inch thicknesses. The 5/8-inch panels are fire-code rated.

High Strength Ceiling Panels
High strength ceiling panels are 1/2" thick but have the added strength to have sag resistance that is the same as 5/8" thick Type X panels and greater than standard 5/8" drywall. This 1/2" thick panel offers a cost savings over 5/8" thick panels. Don't use these panels in high moisture areas.

Factory Decorated Drywall Panels These 5/16" thick drywall panels are for factory application of decorative finishes, and are used in prefabricated and modular housing, offices & commercial applications. Refer to Table 1 for widths and lengths.

Sound Deadening Panels
Use sound deadening gypsum panels with Type X fire resistant panels for attenuating transmitted sound. Refer to Table 1 for widths and lengths.

Tile Backing Panels
Use tile-backing panels to install tile on for high moisture areas, including showers and counter tops. The panels are a glass mat and water-resistant gypsum combination. It is also available in Type X rating for added fire resistance. Refer to Table 1 for widths and lengths.

Exterior Sheathing Exterior drywall sheathing panels are designed for indirect exposure to the weather and installation on vertical surfaces. Their water-resistant core is covered by tightly bonded, water-repellent paper or in a paperless style with embedded fiberglass facing and primer coating. Using these panels eliminates the need for sheathing paper. They also add to the fire resistance of the structure. Apply the sheathing panels directly to the framing members of a building.
Exterior drywall sheathing must be covered with an exterior finish. Aluminum, stucco, masonry and shingles are all suitable finishes. Be sure to attach the finish to the framing members, not just the sheathing.
Exterior sheathing panels come in 5/8- and 1/2-inch thicknesses. The 5/8-inch thickness is fire-code rated. The 1/2-inch panels are available in 2-foot widths that have V -shaped, tongue-and-groove edges, as shown in Figure 1-2. Apply these panels horizontally on vertical surfaces. The V-grooves aid in the shedding of water.
The 4-foot wide panels normally have square edges. You can install these panels with the long edges vertical or horizontal. Refer to Table 1 for widths and lengths.

Backing Board
Gypsum backing board is designed to serve as the first layer in a multi-layer gypsum wall or ceiling. Both surfaces of backing board are covered with liner paper and are not suitable for a decorative finish.
Backing board is also available with a foil backing. And there's also a moisture-resistant backing board that has a vinyl covering. This is intended for high-moisture areas, such as showers, where tile is applied over the backing surface. You must seal the cut edges of backing board to keep it water resistant.
Backing board is 4 feet wide and 8 to 12 feet long. It's available in 1/2- and 5/8-inch thicknesses. The 5/8-inch thick panels are fire-code rated.

Gypsum Coreboard
Gypsum coreboard is 1 inch thick and is designed for solid gypsum partitions without framing members. It consists of two factory-laminated layers of 1/2-inch gypsum backing board. Coreboard is manufactured with V-shaped, tongue-and-groove longitudinal edges for use in solid partitions. See Figure 1-3.
If you're putting up partitions with spaced core sections, order coreboard with square edges. Square edge core board comes scored at 6- or 8-inch intervals so it breaks easily into sections.

Gypsum Formboard
Gypsum formboard panels are used as the form for poured gypsum concrete roof decks, Leave the formboards in place after the gypsum concrete sets up. The formboard serves as the ceiling surface in the finished installation. Gypsum form boards are faced either with manila paper suitable for decorating or with vinyl that needs no other finishing.
Fasten the formboards to the beams or joists and then pour gypsum concrete into the form. The combination of formboards and gypsum concrete creates a non-combustible roof. The formboards aren't considered structural members for purposes of calculating the load-carrying capacity of the completed roof. Formboards are 1 inch thick, 8, 10 or 12 feet long, and come in widths of 24, 32 and 48 inches.

Gypsum Planks
Gypsum planks have steel reinforcement for use as structural roofing members. A galvanized wire mat is cast into the planks, and the planks have galvanized steel tongue and groove edging. They're not water resistant, and so should be covered with roofing as soon as possible after installation. Gypsum planks are 2 inches thick, 15 inches wide and 10 feet long.

Gypsum Lath
Gypsum lath can be used as the base for plaster on walls and ceilings. It consists of a gypsum core covered with rough paper that creates a good bond with the plaster. The top layers of paper absorb moisture quickly and evenly from the plaster, so that it will set up properly. The paper near the gypsum core is moisture resistant to protect the core. Installation is quick, and it provides a smooth, continuous surface for the plaster.
Lath is available with a solid face or a perforated face. The perforated face has 3/4-inch holes drilled through the board at 4-inch intervals. When you use perforated lath, the plaster is forced through the holes. This increases the bond between the plaster and the board. It also increases the fire resistance. Gypsum lath is available 3/8-inch and 1/2-inch thick, 16 and 24 inches wide, and in lengths of 4 feet and 8 feet.

Partition Blocks
Solid gypsum partitions use partition blocks rather than studs for framing members. Partition blocks come in 2- to 6-inch thicknesses. The precast blocks are 12 inches high and 30 inches long. These blocks are made from a mixture of gypsum and fibers. Fibers are added to increase the block strength. Laminate standard gypsum wallboard to both sides of the partition blocks to form the finished wall or partition.

Radiant Heating Panels
Gypsum radiant heating panels have electric resistance heating elements embedded in the core of each panel. You can install these panels in suspended ceilings or use nails or screws to fasten them directly to joists. When using radiant heating panels in walls, fasten the panels directly to the studs.
The panels are 5/8-inch thick and have long electrical leads that connect to a circuit by means of a junction box. The panels come 4 feet wide and are 4, 8 or 12 feet long.

Pre-decorated Drywall
Pre-decorated drywall is standard drywall covered with decorative paper or vinyl. It's available in a variety of colors, patterns and finishes. You can install it with color-matched nails or adhesive. It requires no further finishing after installation.
The panel edges are either tapered or square and are butted together. It's harder to make good joints between these panels. That's why you won't use predecorated panels for ceiling applications. Sometimes special moldings are used to conceal the joints.
Matching or contrasting moldings are available for pre-decorated drywall panels. Use these moldings to cover and protect corners and panel joints. Moldings help protect the panels from damage.

Veneer-Base Drywall
Use gypsum veneer-base drywall, also known as blue board, when you want to apply a veneer plaster coating to the surface. Veneer plaster is suitable for all interior applications.
Veneer finishes are durable and wear-resistant. Use them in the heavy-traffic areas of a building. You can apply the veneer coating in one or two layers. You'll apply it 1/16 to 3/32 inch thick, directly to the drywall. The finish can be either smooth or textured.
Gypsum veneer-base drywall is covered with multiple layers of paper that provide strong adhesion to the veneer plaster. The outer layers of paper absorb the moisture from the plaster, ensuring a strong bond. The inner layers of paper are moisture resistant to keep the gypsum core dry.
Veneer-base drywall comes in 4-foot widths with square-cut edges. Standard veneer-base drywall is 3/8-inch, 1/2-inch or fire-resistant 5/8-inch thick Type X. Install it with nails, screws, or adhesive. Refer to Table 1 for widths and lengths.

PANEL EDGES
So far we've concentrated on panel core compositions and surface coverings, but that isn't the whole story. Now let's take a look at the panel edges.
Unfinished panel edges need special treatment. Exposed, unfinished panel edges should have trim or comer reinforcement installed. Butted panel edges may require expansion joints to prevent buckling in warm and humid weather. Let's look at each of these panel edge treatments.

Trim
Exposed, unfinished panel edges are common at window and door openings. The two most frequently used panel edge trims are metal trim and vinyl trim.
Metal trim- This comes in U and L shapes. Apply it to exposed edges of drywall to protect it and give a finished appearance. Fasten the trim to the drywall by nailing through the flange of the trim. Flanges are available in solid metal or in mesh. Cover the flanges with joint compound or veneer plaster,
Vinyl Trim- Apply vinyl trim to drywall edges and intersections. You can use it as a decorative finish for exposed edges, or you can use it as a flexible seal in place of caulk. It can also provide stress relief at the edges of panels.
Vinyl trim comes in a variety of colors and can be painted. There's even vinyl trim that looks like wood. It's more economical than clear grade wood. And it's more resistant to damage and wear.

Corner Reinforcement
Corner reinforcement, also known as corner bead, protects external corners from damage. Apply it to external corners that are subject to wear.
Corner bead is made of metal, so it's stronger than the edges of the drywall. You can buy it in solid galvanized steel or wire mesh galvanized steel. It's V-shaped and has an angle of slightly less than 90 degrees. A raised section, or bead, at the bend of the "V" provides protection against impact damage. The bead also serves as a screed or guide for the drywall knife, aiding in the application of joint compound. Each half of the "V", called a flange, is from 1 to 1-1/4 inches wide, depending on the particular corner bead.
You can nail or staple the corner bead into place. Or you can use a special clinching tool. This tool drives parts of the flange into the drywall to hold the bead in place. Use wire mesh corner bead with veneer plaster. Use the solid steel corner bead with all types of drywall construction.

Expansion Joints
Where there are large expanses of ceiling or wall use expansion joints to relieve the stress caused by expansion and contraction. On ceilings, install expansion joints from wall to wall. On walls, install them from door header to ceiling or from floor to ceiling.

Most expansion joints are made of formed zinc so they won't rust. They fit between the drywall panels. The center section of the expansion joint is V-shaped. The "V" is flanked by two flanges. Cover the flanges with joint compound or veneer plaster.
For radiant heating systems, there's an expansion joint with flanges that fit behind the panels. When you use expansion joints in systems that have special sound control requirements, you'll have to install seals behind the joints.
That's about all you need to know about drywall materials. There's no need for you to memorize the information in this chapter. Just remember where you read it so you can look up what you need to know when a question comes up on some job. In the next chapter we'll take a close look at some of the specialized tools drywall hangers use to speed and simplify the work they do.

Introduction | Table of Contents | Back Cover