How to Shim Behind Drywall With Cardboard Drywall Shims

Man Installing Drywall

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In new-construction home building, you hang drywall on studs and presumably all of the drywall edges meet perfectly with each other and with all the window and door trim. If the carpenters have framed the walls properly, the drywall installers will have a perfect surface for installing drywall. But when you are remodeling a home, often you will not find a perfect nailing surface for drywall.

When Studs or Joists Are Unacceptable for Drywall

In home remodeling, not all is perfect because you are dealing with the consequences of time, demolition, or even poor decisions made decades ago by builders and homeowners.

Often, after you have removed the older drywall or plaster, you will find individual studs or joists that are warped, twisted, and bowed. This is especially common when the previous wall covering was plaster since the lath-and-plaster system is excellent at compensating for imperfect stud assemblies.

Sometimes, the very act of removing old drywall will bring studs out of line when over-ambitious workers knock studs slightly back. Another condition is when a number of studs, even if they are in good condition, are not far in or out enough to match your other work. This section of studs might be just 1/8-inch back from an adjacent section of studs.

Do you accept the imperfect and go on? Or is there a simple way to nudge it along until it is close to perfect? The answer is drywall shimming. Far from being technological marvels, drywall shims are dead-simple, cheap cardboard strips sized perfectly for studs.

Those warped, twisted, and bowed studs benefit from shimming partial sections. The occasional stud that is too far back can be shimmed from top to bottom. And that entire section of studs that doesn't match its neighboring section can be shimmed forward 1/8-inch.

Drywall Shims Basics

  • Drywall shims are strips of cardboard that increase the forward reach of a stud (that is, the stud's width) so that the drywall hangs better on the stud.
  • Drywall shims are not to be confused with window or door shims, which are short, tapered, and made of wood or plastic.
  • Since they are constructed of water-soluble cardboard, drywall shims should never be used for framing windows or exterior doors. Also, they should not be used for plaster work since the water from the plaster would cause the shims to become pulp-like.
  • At 45 inches long, drywall shims are the perfect length because they are the width of a sheet of drywall or half of an 8-foot length. In either sense, shims are cut perfectly to size for working with full sheets of drywall.
  • At 1 1/2 inches wide, drywall shims are the width of a stud, reducing width waste and the need for long cuts.
  • At about 1/8-inch thick, drywall shims are thin enough to correct shallow irregularities but can be stacked to address worse problems.
  • Hard cardboard that does not compact under pressure is the source for drywall shims. Other materials, such as corrugated cardboard, would compact too far.
  • While drywall shims can be duplicated for free by slicing up old cardboard, veneer board, or even tar paper, cardboard drywall shims are far easier to work with.

Tools and Materials for Installing Drywall Shims

  • Cardboard drywall shims
  • Staple gun and staples
  • Laser level or chalk line
  • Pencil
  • Drywall installation tools

How to Install Drywall Shims

  1. Use a chalk line or laser level to determine how much the defective joists or studs need to be shimmed for the drywall. If dealing with a section of defective studs or joists that are all different distances, write individual measurements on each stud or joist with a pencil.
  2. Lay a shim (or multiple shims) against the stud or joist until it reaches a point consistent to the level point. 
  3. With your staple gun, staple the shims in place against the stud. Generally, shims are less effective beyond three or four of them, because the staple is not long enough to reach the stud. Another reason is that the eventual drywall screw or drywall nail will have less wood to grab onto.
  4. Continue installing drywall shims for all of the studs.
  5. Make one final check for level by using your laser level or chalk line.
  6. Install the drywall as normal, using a drill, drywall screws, and drywall.

Where to Find Drywall Shims

Most large home improvement stores will carry 100-count bundles of drywall shims in the drywall section of the lumber department. The shims will typically be located in the tools and accessories section of this drywall area. Because they are not commonly used by homeowners, drywall shims might be on a higher shelf or away from immediate view.