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Drywall, also known as gyproc, Sheetrock®, plaster board, gypsum board, to name a few, is a very popular method of applying a wall or ceiling finish. It is quite inexpensive and is easy to install and paint. Its only draw back, for the novice, is the requirement to apply drywall joint compound, we call mud, and sand it down smoothly. The following article will help you understand the principles of finishing drywall.
The term drywall comes from the early days when tradesmen used to apply the wall and ceiling finish onto wooden laths with a mixture of sand, cement, lime and water. They referred to it as plastering a wall or ceiling. They still have these specialized plasterers today, but we can have the advantage of a plaster wall or ceiling put on dry in ready made sheets. Thus the name drywall evolved. The sheets are placed across the studs or joists rather than with their length running with the studs or joists. The sheet is cut to length by scoring the paper layer with a utility knife, snapping the board in a 90 degree angle towards the back and cutting the back paper layer using the inside angle of the break as a guide. To cut round holes for plumbing or square holes for electrical boxes or such, a drywall saw is used. Measure the location on the face of the drywall and just push the stiff, short blade through the drywall and commence cutting.
Drywall comes in many applications: regular drywall for walls, moisture resistant for walls called green board, ceiling board, which is still 1/2" thick rather than the required 5/8" thickness for the ceiling when the joists, rafters or trusses are on 24" centers, is sag resistant. I like the ceiling board because it is lighter than the 5/8". It also comes in a 5/8" fireguard thickness, used mainly in commercial applications.
Before starting to apply drywall tape and mud, make sure all the drywall screws or nails are set below the surface a bit. Don't go through the paper of the drywall sheet, just depress the screws or nails below the surface. The screws are best installed with a drywall screw gun meant for this purpose. It has an adjustable chuck on it with a clutch that slips when the screw is just below the surface. Do-it-yourselfers can purchase a less expensive dimpler that can be used in a regular variable speed, reversing drill. Most of the new rechargeable drills have built in clutches, designed for this purpose, as well. Screws are the best option over nails. Ask for proper drywall screws by name, use # 6 x 1 1/4" long screws for 1/2" drywall on walls and 1 5/8" drywall screws for 5/8" drywall on walls and ceilings as well as 1/2" ceiling board on the ceiling. If using nails use 1 3/8" drywall nails for 1/2" drywall. Nail them in pairs every 12" in the middle of the board and 6", along the ends of the board. Along the edges, nail two nails in at every stud or ceiling joist. Nails are set with the hammer forming a dimple below the surface. There are drywall hammers available that have a textured square head ideal for this purpose. It looks more like a shingler's roofing hatchet than a hammer. Screws are placed in the same configuration as the nails, but in singles only. Keep the screws and nails about 3/8" to 1/2" away from the edges. Outside corners should be covered with a corner bead either nailed or screwed on or applied later with the mud application using a mud-on corner bead. I prefer the metal corner bead, unless the corner is rounded where special beads are made for this purpose. Make sure the metal part of the bead is below the bead itself. You can bring the bead above the surface of the drywall by adjusting the metal in or out on that side. Check with a tri-square to make sure the blade of the square will not touch the metal or any of the nails. You want the bead to be slightly higher than the surface of the metal band. In other words don't nail the corner bead too tight on the corner.
There are two choices of tape to use to cover the drywall joints in a wall or ceiling. The professionals use the paper tape and wet it thoroughly with a mud paste before installing it in the joint. To get the paper tape wet, without purchasing the expensive tube applicator that the pros use, I actually cut the desired length off and put it into an ice cream pail to absorb some water for a few minutes. While the tape is soaking, apply a thin coat of mud, to the bottom of the joint. As the tape is brought out of the pail and onto the wall most of the surface water is wiped off with the fingers. The tape is applied damp over the mud, centered in the joint. The mud is then squeezed through the pin holes in the tape, leaving a skim coat of mud covering the surface of the tape. Use a 6" drywall knife for the application of the mud and tape. You will notice that the drywall edges are compressed to form a groove when placed together. This is designed to accept the mud and tape for the first application. The 6" blade spans the depressed joint easily, scraping excess mud off the high point of the drywall. Notice that the ends of the drywall are full thickness, not forming a depressed joint, like the edges. Usually when installing drywall sheets on a wall or ceiling the installer tries to fasten the longest sheet he can to fit into the room without joints. The sheets come in 8, 9, 10, 12 and 14 feet lengths. For a long wall or ceiling, obviously we need to butt one sheet to the other to extend its length. In this case the tape is applied over the joint as before and the mud built up slightly for the first application.
Inside corner joints are the most difficult to apply tape and mud to. For using the paper tape, wet it as for the joints, but as you are extracting it from the pail, bend it forming a 90 degree corner. Notice that the tape actually has a depression in it in the center of the tape for this purpose. There is a special corner trowel that may by helpful to spread the mud in the corner and apply the damp tape bent into the corner. Without the corner trowel, use a 3" drywall knife and apply the mud to both sides of the corner. Don't apply too much pressure here and rip the tape, just enough to lay it nicely into the corner to form a straight line. Try to squeeze the mud out through the pin holes of the tape, as done with the joints, leaving a skim coat over the tape. This is as far as you go with the inside corners for the first application.
Outside corners are quite easy to apply the mud to in comparison to the inside corner. With the metal corner bead already fastened in place, take your 6" knife and apply the mud to cover the metal part of the bead, scraping any excess mud from the bead and the other side of the knife. This concludes the first application of the outside corner.
The only part of the drywall sheets remaining to be mudded is the nail and/or screw holes. Using the 3" or 6" knife, again, apply a bit of mud to completely fill the hole, leaving a skim coat covering the surface. I usually carry a phillips screwdriver in my back pocket, in case a screw is projecting slightly above the surface of the drywall. This is the time to give it a slight turn to embed it below the surface. Re-do the mud over it and leave it to dry.
Drying time varies with temperature and humidity in the room. The thickness of the mud is the greatest in the inside and outside corners for the first pass, so these places take longer to dry rather than the screw holes and joints. Overnight is the minimum amount of time to let the mud dry. If drying is taking forever, open a window and get some air movement, a slow moving electric fan helps out, too. Before the next application of mud the walls and ceiling are sanded lightly. Sanding can't take place until the mud is completely dried. The pros usually leave their sanding stage till the end. They usually knock off the high points with a large drywall knife and carry on with more mud. I recommend, until you gain the experience, to sand slightly between coats of mud. This will end up in a better, smoother job overall. Try to control the need for sanding the mud down to the drywall. This is not the result we want. Sand the high spots off and taper or feather the mud off toward the surface of the drywall. Remember to wear safety glasses and a dust mask while sanding. Clean up the dust right after sanding to keep it contained in the room you are working in. Poly (6 mil vapour barrier, polyethylene sheeting) over openings and air ducts and close doors to help in the dust confinement. For large openings a great little zipper device is available to be taped onto the poly in an opening. With this zipper you have easy access in and out of the room.
I mentioned two choices of tape, I like to use a fiberglass tape for drywall repair and new construction. It is self-stick, about 2" wide. For repair work, remove any loose paint, paper or tape. Sand the area about 6", at least, on each side of the crack or defect. Lay on the tape, dry, centered on the crack, no mud. Now with a 3" or 6" putty knife lay the first coat of mud on. Press it through the tape and leave a built up layer over the tape, just enough to cover it. Don't be too fussy with getting it smooth here, try more to build up the thickness of mud over the tape evenly. Leave it for 8 hours, at least, until dry. Sand down high spots only. Don't sand down to expose tape. No worries if you do, just build up the mud again.
After the mud has been left overnight and is thoroughly dry and the sanding stage has been completed, the second application of the mud can begin. The next application of mud should be with a 6" drywall knife over each side of the inside and outside corners and the screw holes. For the joints, use a 12" drywall knife, extending over the previously done joint by about 2" and feathering it out over the edge of the existing mud. Get into the habit of applying pressure on the feather edge and no pressure over the tape. You do this with a twisting of the drywall knife. Do this to both sides of the tape. I like to use a ready mixed drywall joint compound
that comes in a plastic pail. If the mud in the pail is too dry add some water and stir it up using a drywall mixer
in the chuck of a 1/2" drill.The main problem with novices is not putting on enough mud. Have the trowel
edge covered with mud, apply it with a drywall knife almost square with the wall or ceiling, then slowly reduce the angle as you draw the mud off the knife. After a few practice strokes, you'll get the hang of it. See the drawing.
Wait 8 hours again to dry. Sand very lightly, just to remove any ridges. Sometimes a third coat is required, just to fill in any air holes or slight depressions that may have been left. Sand when dry. Vacuum any dust on the wall. Prime with a Latex Drywall Primer-Sealer.
You may notice slight imperfections after applying the primer/sealer. This is normal. Just go over the imperfections with a skim coat of mud, let dry and re-coat with more primer sealer. At this stage the mud and sealer dry quite quickly, so much time is not lost. Make sure you prime the fresh mud, though, or the finish coat will look blotchy. When the primer/sealer is dry apply two more coats of your choice of colour and paint, latex or enamel, on the walls and ceilings. You will find that the flatter the finish on the surface the less likely any imperfections will show. Too flat a surface doesn't wash very easily, so the best choice for paint sheen is an eggshell finish.
Stand back and admire you work, checkout your pocketbook, too, for all the money you saved.
