Is my plan to replace interior doors reasonable?

Question

I bought some pre-hung doors, intending to replace several interior doors. The problem is, the existing door jambs are shallower than usual -- I think 3.5" instead of 4.5". So if I simply remove the old doors and install the new pre-hung doors, I'll need to build up the frame or something to attach the casing. Seems like a big hassle, and not likely to look good.

So I thought maybe the best plan would be to leave the frames in place, but replace the doors. I figure:

1. Remove the hinges from the existing frames
2. Use wood putty to fill the spots where the hinges were (is this a mortise?)
3. On the new door, measure the location of the hinges
4. Use the hinges to draw a template on the existing frames
5. Drill pilot holes for where the screws will go on the existing framse
6. Use a router to mortise the hinge template
7. Screw in the hinges
8. Hang the door
9. Beer

I'm obviously 99% clueless so if this is a terrible plan, please let me know.

Answer 1

There's nothing inherently wrong with your plan aside from the massive amount of work needed. With good technique, a high level of precision, and the proper filler material you can arrive at a good outcome, but it would be fussy work. If you're up for that, have at it.

Another probably easier option is to disassemble the jambs, rip them in half behind the stop location, and remove material to shrink the jamb depth. Then reassemble. The surgical scar will be hidden by the stop. (Modern jambs are usually veneered and radiused.)

If you happen to have solid wood jambs (very rare in my experience), you could simply rip off one side and re-sand the face, but that may actually be more work.

Disassembly usually starts with popping the stops off. They're usually shot on with trim nails. Pull the nails through from the back side with a locking or channel pliers. Then gently knock apart the corner joints in the direction of their nails.

Be sure to size your jambs to the largest wall thickness in each case. Your trim will be easier to fit then. Reattach the jambs however you like so that the fasteners are hidden by the casing. Trim nails and glue work well, but the ideal solution may be pocket screws. Inexpensive kits make that easy. Screws don't wiggle loose and you could forego the glue. Glue is usually a good idea, though.