If I'm understanding the situation correctly (which I'm not altogether sure)--it sounds like you could build it up with a shim.

Do you have access to a table saw? You can rip 1/4" strips to fit the gap. Put those up, then attach finish molding to those.

Regards,

-k2 in CO

Moderator, Miscellaneous Forum

http://www.bobvila.com/BBS/Miscellaneous

already pre-exists (1/4" rounded edge or 90 edge). for your application. Check out the mouldings display/catalogue at your local supply.

one attaches the "extension jamb" moulding to the "exposed edge" of the jamb and "builds it up" to the surface of the wall surface. Then one can install casing with no reveal, or your desired reveal (1/8", 1/4", whatever) as normal. Usual "basic" extension jamb is easily found in clear pine and red oak, other materials may need to be ordered, as are usually not "stocked". Square edge, rounded edge (radius 90 degrees), "ranch style" (eased rounded edge - kind of tapered more one side of the corner than the other) are the usual "stock" finds. Usually found in 1/4", 3/8", 5/16" (sometimes has to be ordered but not special set-up charge), 1/2", and 3/4" easilly. I have usually had to resort to making my own 5/8" when needed out of clear pine stock and a router edge and rip to depth as is a size not usually found and us usally a set-up charge that is cost prohibitive in my "little" projects. The two big box store chains (HD and Low_s) usually stock in clear pine and some sizes in red oak, but other sizes and wood species are special order.

be sure to pencil mark your extension jamb nailing locations on the inside of your jamb so as to avoid hitting those fasteners when you attach your casing front edge. Also, if hardwood like oak, pre-drill your holes to avoid splitting the jamb and your trim moulding.

If your local box store doesn't have extension jamb in 1/4 thickness, another idea is to get 1/4 door stop and rip off the finished edge to match your trim (clear pine or oak or whatever). at 1/4" if clear pine you could even rip this with a jigsaw just use the cut edge towards your wall and the finished "stock" edge towards the exposed edge of your jamb, as the "ripped edge will be hidden by your door trim casing.