Gilles' Outlet

March 26, 2007

Installing door casing

Filed under: Finish Carpentry — Gilles @ 6:05 am

Door jambs are prepared. Molding is cut to length and installed.


Skill Level: 2 (Basic)

Time Taken: About Two Hours

Finish carpentry is very rewarding because results are highly visible.

Left: the door around which casing will be installed. The yellow substance around it is expanding insulating foam. It was allowed to cure over several days. It prevents cold air infiltrations around the door frame.


Right: the molding we will use. It is pre-primed MDF and was purchased at a local lumberyard for about $3 a piece.

Before installation, it received two coats of good quality satin latex paint. 

Left: close-up detail of the bottom left door jamb. I decided to install the molding all the way down to the plywood step at the bottom. The molding will need to be cut to clear the fondation.


Right: close-up detail of the bottom right door jamb. The molding will have to be cut on the right side too.

Left: I marked a 1/8” reveal (amount of the jamb edge that will be visible) using a combination square. This $15 tool is worth every penny.

It is only necessary to mark the top corners.

Right: I measured the width of the door opening. That is the inner distance between the left jamb to the right jamb. It ended up being 31 1/2”

I measured the width of the molding. It was 2 1/4”. I calculated the length of the top piece of casing along the longest side by:

L = Door Opening + (2 * Reveal) + (2 * Casing Width) = 31 1/2 + 1/4 +  4 1/2 = 36 1/4”

I always use the longest edge when miters are involved. It is much easier to hook up the tape measure to the longest edge of the piece. 

Left: I used a power miter saw to cut a 45 degrees miter at one end of a piece of molding.

I hooked up the tape measure to the longest end of the miter and marked 36 1/4”. I used the miter saw to cut the second miter to length.

It is easy to cut the miter on the wrong side so do not hesitate to make a sketch on a notepad before actually cutting.

Right: The top piece cut to length. It is exactly 36 1/4” on the longest edge, that is the top edge on the picture. 

I checked the drywall around the door to ensure it was flush with the door jamb. It was flush. 

If the drywall is not flush with the door jamb, there will be large gaps between the wall and the molding. When faced with this situation, I peel the drywall paper at high points and use a rasp to remove enough gypsum for the wall to be flush with the door jamb so the casing can rest flat on the wall and the door jamb. This kind of attention to detail is what makes the installation look "professional".

Some carpenters just caulk these gaps but the result does not look as good.

I positionned the top piece in place and made sure the reveal was the same everywhere. I used a pneumatic nailer to drive 1” brad nails (18 gauge) in the door jamb because they need to penetrate the door jamb to hold.

Nails are usually driven in a groove of the molding. This helps conceal the small hole left by the brad nailer.

I first secure a corner and then the other corner. I then drove a few more brads in between. That is approximately 4~5 brads total.

The top of the molding should be secured to the framing with 2” 16 gauge finish nails. This requires me to switch nailers so I’ll do it later.

Left: for the right piece of the casing, I cut a piece of molding 1” longer than needed.

I laid the necessary notches with a pencil and used a Japanese pull saw to notch the molding. A pull saw cuts on the pull stroke. It is easy to use and mine is fine toothed so it makes very clean cuts.

Right: The bottom of the molding after the cut was finished.

I prepared and cut the left side the same way.

I then positionned the left side and aligned its miter with the miter on the top piece. I checked the reveal was about the same over the whole length. I secured it using brad nails, starting with the top corner then the bottom. I added about 6 brad nails in between, spaced at regular intervals. I repeated the procedure for the right side of the door.

Left: I used a pneumatic finish nailer with 2” 16 gauge nails to secure the molding to the house framing. I drove about 4~5 finish nails equally spaced.

I repeated the procedure on the right side of the door. I also secured the top piece with about 3 finish nails.


Right: the finished door. Nail holes were filled with lightweight spackling paste. The paste was left to dry and paint touch ups were made after a light sanding.

It is also possible to fill nail holes with caulk, for instance DAP Alex Plus Siliconized Latex caulk.

Left: detail of the bottom left of the door with the molding installed. It fits snuggly around the fondation.


Right: detail of the bottom right of the door with the molding installed. It fits snuggly at the hinges and around the fondation.

Tools Used:  

  • Power Miter Saw
  • Pneumatic Brad Nailer
  • Pneumatic Finish Nailer 
  • Tape Measure 
  • Basic Carpentry Tools

Materials Used:

  • MDF Molding (3 x 7ft)
  • Finish Nails (2”, 16 gauge) 
  • Brad Nails (1”, 18 gauge)
  • Sating Latex Paint
  • Splackling Paste
  • 400 grit sand paper


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