How to Install Case Molding on a Doorway Opening

Adding case molding to a doorway opening serves aesthetic and structural purposes.
A casing helps secure the door frame to the wall. In fact, without a case molding, a door might become misaligned without such support. Additionally, case moldings hide imperfections of a doorway area. For example, if a wall's thickness is unequal, applying a case molding can easily solve this problem. With a little bit of time and the proper tools, installing case molding can be uncomplicated.

Step 1

Measure and pre-cut all of the casing pieces that need to be applied to the door opening with the carbide finishing blade.

Step 2

Cut the longer lengths of the casing pieces before the successively shorter pieces with the carbide finishing blade, so the casing material is used most effectively. For a better fit for polyurethane molding, Burton Mouldings advises to cut all of the casing pieces 1/8 inch longer than the needed measurement and applying the casing end pieces onto the wall first and the middle pieces last.

Step 3

Place the cut pieces against the wall proximal to their desired locations. For polyurethane case molding, always apply a continuous line of polyurethane adhesive on the wall before finally adhering the casing. Nail the casing pieces into place with a 1 1/2-inch nail. Nail both sides of each casing with a nail--one into the door frame, and one on the other side through the drywall into the rough framing. The nails must be applied within an inch of the ends of the casing, but not too close as to risk cracking the casing. According to Burton Mouldings, a lot of carpenters apply an extra small nail through the top corner of the casing, which is beneficial if done without cracking the casing.

Step 4

Glue the corners of the casings. White glue, or PVA glue for poly vinyl products, is the best for casing, says Burton Mouldings.

Step 5

Fill the open spaces, or joints, with a paintable siliconized latex caulking. Fill any empty nail holes with a lightweight auto body filler or a lightweight gypsum filler. Two or three coats is typically enough. Finish the joints with care and effort, as they are near eye level and easily seen. Wipe any extra filler or caulking away with a damp cloth.

Step 6

Sand the surfaces of the moldings. Be careful not to sand too much, as this might remove the protective layer. Sanding too much might also result in having to apply filler and sand all over again.

Things You Will Need

  • MDF molding or polyurethane molding
  • Measuring tape
  • Hammer or nail gun
  • Triple-chip carbide finishing blade
  • 1 1/2-inch nails
  • PVA glue
  • Polyurethane adhesive
  • Lightweight sanded auto body filler
  • Paintable latex caulking
  • 80-grit garnet sandpaper
  • Damp cloth


  • Rooms with tall ceilings generally need 3 1/4-inch door casings. Doors 8 feet tall need 4-inch or 4 1/4-inch door casings or larger.
  • A contemporary casing design typically calls for casing that wraps entirely around the doorway. In this instance, the corners are cut at 45 degrees.
  • A more upscale, traditional casing design might suggest decorative molding, otherwise known as headers, which ornament the top of the door. With this design, casings are used only as trim along the outside of the door.
  • An added block, also called a plinth block, is utilized sometimes at the bottom of the door. The casing then is applied on top of the plinth block.
  • Square, decorative blocks called rosettes are utilized on the top corners of casings instead of a header. Their designs range from highly complex florals to simple, flat, smooth blocks. A plain succession of circles engraved into the face of the block is the most common type of rosette.

About the Author

Jessica Lutjemeyer is a copy editor at "Willamette Week" and began writing professionally in 2008. Her work has also appeared in "The Arizona Republic," "The State Press" and "The Cronkite Journal," among others. Lutjemeyer holds a bachelor's degree in journalism from Arizona State University's Walter Cronkite School of Journalism and Mass Communication.