Hanging drywall is often one of the first tasks taken on by the novice renovator. Plasterboard or Sheetrock, to call it by one well-known proprietary name, has become perhaps the most common walling material in this country. It’s easy to use, relatively inexpensive, offers some soundproofing and insulation, and, when properly installed, results in a smooth and handsome surface.
Drywall comes in sheets. It consists of a core of a plaster-like material (usually gypsum) sandwiched between layers of paper. The sheets are four feet wide and of various lengths (eight-, ten-, and twelve-foot lengths are common). Thicknesses vary, too, but most building supply yards will carry three-eighths, half-inch, and five- eighths-inch sheets.
The sheets of wallboard are attached to the structure of the walls with specially designed drywall nails or screws and sometimes with adhesives. Then the joints between the sheets are hidden with a specially made drywall tape (either a fiberglass mesh or paper tape) followed by several layers of a premixed, plaster-like material called joint compound. Or, in some cases, the entire surface is coated with a skim coat of joint compound or even of traditional plaster.
The kind of drywall used varies, depending upon the location and eventual finish to be applied. Standard wallboard has a smooth, gray surface. Sheets with a greenish hue have a vapor barrier of fiberglass within for installations (like bathrooms) where the amount of moisture will be high.
The blue-tinted wallboard is designed to be skim coated. Fire-resistant wallboard is also available.
Here are the tools of the trade, and some basics on how to use them to patch and finish wallboard surfaces.
Surfoam. This tool is a relative of the file. It has a hollow aluminum frame with a steel blade. The replaceable blade is perforated, with individual raised teeth called rasp teeth.
The tool can be used to smooth wood but is particularly useful when hanging drywall. It will remove irregularities from the edge of a piece of wallboard that has been scored and snapped. It can also be used to shave down a piece slightly, or to finish a hole or slot cut in the board.
Surfoams are sold in one-handed and two-handed sizes. The smaller surfoam is about the size of a block plane, five or six inches long. It’s held in one hand, freeing the other to hold the workpiece. The longer surfoam (its blade is ten inches long) is most effective when used with two hands. The extra length helps flatten out long, wavy cut lines.
Drywall T Square. Also called a wallboard T square, the drywall T square has a four-foot blade in order to reach across the width of a standard sheet of gypsum board. The crosspiece at the head is shorter than the blade (typically less than two feet), but it resembles a draftsman’s T square in being offset slightly so that its lip butts to the edge of the wallboard. The length of the blade and the crosspiece are marked with dimensions in inches.
The T square is intended as a cutting guide, though it is also useful for marking holes to be cut in the interior of sheets of plywood as well as wallboard. When used for marking gypsum board, a utility knife is positioned flush to the side of the square and cuts a score line through the top layer of paper on the wallboard. The core of the piece will then snap when it is bent away from the score line, after which the backing paper is sliced with the utility knife.
While wallboard can certainly be marked using a chalk box and cut freehand, using a drywall T square makes both marking and cutting faster and more accurate. The two-inch wide blade is exactly the same width as plug boxes, so both sides can be cut without the square having to be moved.
Taping Knives. At first glance, taping knives look like oversized scrapers, with wide blades and wood or plastic handles. They are known by several names (drywall knives, taping knives, filling knives, finishing knives, and so on) and come in a variety of sizes.
Taping knives differ from scrapers in that they are more flexible. They are used to apply joint compound, the premixed plaster-like substance, purchased in tubs, that is used to finish the taped joints between sheets of drywall. The application process varies from tradesman to tradesman, but typically two or three coats of joint compound are applied, each being allowed to dry before the next is put on. The first coat is applied with a narrow blade (perhaps four inches), the later coat or coats with blades of increasing width.
To make the explanation easier, I’ve divided the drywall knives into three categories distinguished by blade shapes and sizes.
Broad Knives. The flat drywall knives with narrow blades (in the four- to six-inch range) tend to have blades that curve into a roughly triangular shape. They’re used for the first coat of joint compound or for patching jobs.
The Finishing Knives. The flat knives with wider, rectangular blades (eight to 14 inches wide) are used for finishing. Also called taping knives, these are usually sold with blue steel or stainless steel blades to resist rust.
An alternative to a scraper-shaped finishing knife is a purpose-made finishing trowel. It resembles a plaster trowel, but has a slight bow in its blade to allow for the buildup of compound at the seams between sheets of wallboard. The trowel design is more expensive than the knife; which configuration is better is largely a matter of the user’s personal preference.
Corner Knives. As the name suggests, these tools are for corners. They have flexible blades that are bent at a 90-degree angle, permitting the application and smoothing of compound to corners; different models are sold for inside and outside corners. (Without such a knife, inside corners in particular must be done in two steps, with an overnight wait for the compound to dry.) In practiced hands, these knives produce smooth, finished corners.