Ideally, you have carefully inspected the 2 x 4 studs that were used to frame your walls, making sure they were perfectly straight before installing them. But perhaps you weren't as careful as you should have been, or maybe you had the wall framed by someone else, planning to do the drywall installation yourself. Either way, you have a bit of a problem if you find that a wall stud is bowed so it is not flush with the plane of the other studs. It will be hard to install a flat drywall surface if the front edges of all the studs are not aligned in the same plane.
There are several ways to approach the problem if the stud is already in place and you're not eager to tear it out and replace it with another.
Option 1: Bend the Drywall Sheet
Drywall sheets have some "give" to them, and it is easy enough to bend them slightly to conform to whatever curve is set by the bowed stud. The finished wall will curve slightly, but if the bow is relatively mild, the curvature of the finished wall may not be all that noticeable. Or, if the wall is in a utility space such as a garage or basement, the flaw in the wall may not be all that critical. Over time, bowed studs may even straighten out and the curvature may disappear, especially if the curve was slight.
Option 2: Shim Out the Curve
Another solution is to block out or shim the faces of studs that are recessed behind the plane of the other studs. This can be a tricky task, since it is not always easy to determine exactly where the concave spots are, or how much they need to be shimmed. But with a long straightedge and some patience, you can install wood shims in the lows spots to provide anchor points for attaching drywall with screws or nails. This is usually done with two wedge-shaped shims placed atop one another in opposite directions, which negates the angles on the shims and creates a flat block. Attach the shims to the stud with finish nails, then make sure to anchor the drywall with screws driven at these shim locations.
Where a very flat, smooth wall is needed, this is a good solution.
Option 3: Straighten the Stud
You can actually straighten a bowed stud with the following method:
- With a handsaw or circular saw, cut about 2 inches into the stud at roughly the midpoint of the bow. The cut should be made on the concave side of the bowed area.
- Apply force to the stud, straightening it. Slip a single shim into the triangular kerf section that opened up when you straightened the stud. Cut off any excess shim, using a razor knife or wallboard saw.
- "Sister" the stud with a two-foot-long 2 x 4 brace attached alongside the stud, spanning the cut area. This sister acts as a splint to hold the stud straight and reinforce it.
Note that this method of attaching a short "sister" is allowable only for non-loadbearing walls. It cannot be used for studs in load-bearing walls since the building code does not allow for these studs to be cut. However, in load-bearing walls, you can run a full-length sister alongside the faulty stud after you cut and straighten it. The full-length sister is anchored both to the floor plate (sole plate) and top plate, as well as along the full length of the faulty stud. This essentially replaces the bad stud with a new stud carrying the full load. In such circumstances, some carpenters will sister both sides of the bowed stud with full-length reinforcements.