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Corner Bead Intersection
Installing corner bead is one of the last things you do after hanging drywall, and one of the first things you do before you begin to tape and float (also known as drywall finishing). The purpose for using corner bead is two-fold; first, it gives wall's external corners a nice straight vertical line, and second, it provides a bit of protection from bumps.

Types of corner bead

Corner bead is manufactured out of two different materials. Both are widely available. The older, more traditional corner bead is made of light-gauge, galvanized steel.

Why galvanized? As you might expect, it's to inhibit rust. It stands a good chance of rusting in the long run, and the drywall compound (or mud) is water based. Without a galvanized coating, it would start rusting right out of the starting gate.

I might add here that some steel corner bead has paper on both sides, so installation is a matter of just bedding it on a mudded corner.

The second, newer material that corner bead is made from is plastic (PVC). Plastic has two advantages over steel.
  • It will never rust. Galvanized steel will rust once you get under the surface coating.
  • Plastic is highly flexible. When securing it to the wall's corner, you can twist and shape it to get a proper edge. Stick framing is notorious for warped corners; that's not so much of an issue with metal stud framing, though.
What styles of corner bead are available?

Consumers are demanding more diverse ways to customize their homes, so ou have more drywall corner bead choices than ever before. These are the basic styles commonly available:
  • Standard corner bead: This is the traditional contractor-grade corner bead. It forms a 90 degree angle, and measures 1-1/4" X 1-1/4". Available lengths are 8', 9', and 10'. It's available in either galvanized steel or plastic (PVC).
  • Standard archway corner bead: This is a variation of the regular standard bead. It's cut perpendicular to the length every 1/2" or so (exact spacing depends on the manufacturer). This allows the flexibility to finish arches, such as doorways, window pockets, or case openings. It's available in PVC in 8' lengths.
  • Standard corner bead with paper drywall tape: This is the same as the standard bead just mentioned, except for the drywall tape affixed to both sides. The purpose of the paper tape is to provide the means of fixing the bead to the corner. Simply spread sheetrock compound on the drywall corner, embed the bead in it, and set it with your taping knife. (Hint, hint: this shortcut is not the preferred method in the professional community.)
  • Bullnose corner bead: The style of this corner bead recalls the rounded corners of the adobe architecture of the Southwest. It softens the lines of the home. It has exploded in popularity recently in both new, higher-end homes, and in remodeling projects. The dimensions are 3/4" X 3/4". The available length in galvanized steel is 10', while PVC comes in 8' and 10' lengths.
  • Bullnose archway corner bead: This is just like regular bullnose except that it has the same perpendicular cuts as the standard archway bead as described above.

Corner bead 101

There's no big secret to installing corner bead, but it does take a bit of practice, just like all the other aspects of drywall finishing. The good thing about it is that it's just bead and mud. Hey, it's cheap, and if you're not happy, just yank it off and try again before the mud dries!

One caveat to that: always be careful not to contaminate the mud in your pan with any kind of "chunks" of matter. Otherwise, you'll be dragging little trenches in the mud with your knife. And you'll be sorry. Trust me.

NOTE: There's one important thing to keep in mind with any corner bead: never butt two lengths together unless you absolutely have no choice. The only situation I can think of is that the span is longer than your stock. Don't do it to skimp on material... this stuff is cheap.

Prepare the corner

As with most DIY projects, "If you want to make a silk purse out of a sow's ear, you've got to start with a silk sow." In other words, preparation is the key. Before you apply any corner bead, inspect all your outside corners (inside corners just get tape).

When you hung your drywall, one side of the wall ended up overlapping the other to make the square corner. Now, the overlapping side can be a hair short of the corner and you'll be OK, but it can't extend beyond the corner. The best thing to do is run it just a bit long to begin with, and then fine-tune it with a drywall rasp. The fewer air pockets you have behind the bead, the stronger and more impact-resistant your corner will be.

Be sure there are no drywall screws or nails protruding above the level of the drywall face. You'll see professional finishers not even looking; they just lightly drag the edge of their taping knife across the line of screws. When they hear a "clink", they'll draw their drywall hammer and give the screw head a good whack, driving in the screw and dimpling the paper.

Some finishers give it a tap with the butt of the knife handle. Don't do this -- this tool is not a hammer.

Attaching steel corner bead with a crimper

The best way to attach steel corner bead, if you've got a lot to do, is to use a corner bead crimper and a mallet. This tool is shaped to fit on the outside of the bead, and has a retractable crimping "tooth" on either side on one end.

Simply start near the top, center the crimper, and give the button a solid-yet-controlled whack! The teeth will cut and crimp the metal into the drywall. Slide the crimper down a foot or so, and repeat. Work your way down until you're done.

As you might imagine, this takes a bit of practice to get just the right whacking velocity. Practice makes perfect.

Alternate methods of attaching steel corner bead

You don't have to go to the expense of investing in a crimper and mallet for a small-to-medium-sized project. You can use either drywall screws or nails. This, too, is a case of practice -- perhaps a bit less. When using a drill with a #2 screw bit, or a screw gun, be sure to use variable speed.

Ease the screw in until you feel it bite into the stud. Now, just give it little bumps of juice to get the head below where your knife will pass over when applying mud to the corner. If you go too deep, the bead will tend to twist, and you'll lose your good vertical line.

If you use drywall nails, follow the same logic. Tap them in gently. Whichever method you use, the bead edges also must lie flat against the drywall on both sides.

Attaching PVC (plastic) corner bead

Everything we said about steel corner bead applies to PVC, except that for obvious reasons, crimping is not an option. However, with plastic, you have another option: staples. The idea here is that it's best to shoot the staple legs into the built-in holes in the bead.

Of course, staples don't really have much holding power on their own: they just hold the corner bead in place until the mud squeezes through the holes in the bead and dries. For this reason, I'm not very fond of staples. Also, many times the staples won't seat properly. When you tap them in, they lose even more holding power.

Mudding corner bead

Now that you've got all the bead up, what's the next step?

The first coat of drywall compound. Take a look at the way the bead sits on the corner. At the very leading edge is the true "bead", that little rounded area, then the corner bead flows in a concave fashion down onto the face of the drywall.

You'll want to fill this concave area with mud and build it out gradually, so that if you sight down the wall from the corner, it's straight as an arrow. You won't do it all in the first pass, though: this will take two to three passes, depending.

Use your taping knife for the first pass. As you draw the knife down or up, about 1/4" of the blade should hang off the edge of the bead. Do both sides; you'll end up with a feathered build-up off the front of the bead. Don't mess with it now -- let it dry. Once you're more experienced, you can knife it off, but if this is your first time, just let it be.

Float out the corner

The first thing to do now is get a clean, smooth surface to work with. Using the blade of your taping knife, scrape off the aforementioned feathered build-up. Also take off any high ridges left by the edge of your knife on the first pass. They will be much more obvious now that the mud has dried.

Float out the corner like you did in the first pass, but use your floating knife for this pass -- it's much wider. What you're accomplishing here is "busting out" the corner further from the original concave. Can you see where we're going with this?

Once the mud has dried, and you've removed any ridges, have a look at it. You might be ready for the final sanding... or it might want another pass.

Well, are you done or not?

Each case is different. If it looks "pretty good," then it depends on the texture and paint you're planning to put on the wall. As a general rule, there are two things that will make imperfections stand out.

The coarser the texture, the more the imperfections will be hidden.

Also, the sheen of the paint makes a huge difference. The flatter the paint sheen, the more it will cover up.

I was once involved in building a new middle school. The plans called for no texture at all in the hallways, and very slick, glossy paint in horribly garish shades of orange and blue. Of course, the reason was to facilitate cleaning the walls, but what a construction nightmare!

Here's a trick the general contractor used to find faults; you might try it, too. In the darkened room, shine a flashlight along the length of the wall, impacting it in a parallel fashion, not direct-on. Anything but perfect flatness will show up as a shadow.

Anyhow, the things to remember when installing corner bead are to take your time and to have patience. It's an art, and very few of us start off with a well-defined talent.


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