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by CareyBot

Q: I just read an article on repairing drywall at the joints, which I have a lot of. But in one room the wall is cracked in a diagonal — sort of zigzag — all the way down the wall. It really looks as if I need all new drywall. What do you suggest?

A: Zigzag cracks in a finished wall, either in drywall or in plaster, indicate abnormal stress. The cracks can look like a map of the Nile River, traveling in a somewhat vertical path. Or they can look like a map of the Colorado River, meandering across the wall in a diagonal fashion. Sounds like your wall has headed to Colorado.

In either case, the cause is the same — stress on the wood framing underneath.

Unfortunately, you’re right about replacing the drywall on the damaged wall. It’s failed, and replacement is the only viable option. You could try to cut out the damaged section and replace that, but depending on the size of the section compared with the size of the wall, you may as well rerock the whole wall.

Replacing the whole wall also allows for a little preventive maintenance in the form of diagonal bracing. Before you start, take a look at the rest of the room and try to figure out the source of the stress. Are there diagonal cracks above doorways or window openings in addition to the one in the wall? If so, the cause may be that the building is settling or moving with the fluctuation of moisture in the soil.

Kevin has a stress crack in one of the outside walls of his house. That corner of the house moves as winter moisture expands the soil and the summer heat dries it out. The crack opens and closes like clockwork with the seasons. It’s not that bad, so he’s opted to do nothing. If the cracks get worse, he’ll have to look into reinforcing the corner of the house to mitigate the effects of the movement.

If your diagonal crack is the only one, it’s more likely that the crack was caused when the wood framing cured. Replacing the drywall should solve the problem.

The process is pretty straightforward and, while a bit messy, can be accomplished by a do-it-yourselfer. First, carefully remove the casework from any door and window openings and the baseboard from the target wall. Then comes the fun part: demolition.

Let your inner child out and pound holes in the wall large enough so you can get a hand into the opening and pull the drywall off the wall. Once all the drywall is off, pull all the nails from the studs.

With the wall open, this is a great time to add additional electrical outlets, wall sconces with switches, or an extra phone jack. If the wall is an exterior wall, check for adequate insulation and add it if needed.

As an added precaution, we suggest you install some diagonal bracing at each end of the wall. Metal let-in braces are available at home centers and lumberyards. These are rigid "L"-shaped pieces of metal that are solid on one side and perforated for nails on the other.

To install the braces, snap a chalk line diagonally across the wall from the top plate to the bottom plate. Use a small circular saw to cut niches the width of the blade, called kerfs, into each stud. Put the solid edge of the brace into the kerfs and nail the perforated edge to the studs. This prevents the wall from racking if diagonal forces are exerted on the wall.

After installing wiring or insulation, hang the new drywall.

Match the thickness of the old drywall. It’s probably 1/2 inch. We like to use drywall screws to the hang the rock, although drywall nails work. Beware, though, that nails tend to work their way out, leaving impressions of nail heads on the finished wall. If you use screws, install them about 8 inches apart. If you use nails, 6 inches on center is the standard.

We recommend using fiberglass mesh tape with a first coat of a hot mud, such as DuraBond 90 to tape the joints.

This base coat tends to be stronger and more resistant to cracking than paper tape and standard joint compound. Because it dries harder, it’s harder to sand. Use joint compound for subsequent coats because it’s easier to sand and has a longer pot life.

Once the final coat of mud is sanded, paint the wall using drywall primer and one or two coats of acrylic finish. Reinstall the casework and baseboard and you’re done.


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