I am installing the casing around the windows in my basement and the sheetrock does not exactly line up with the window jambs. My trim carpenter that did the trim on the main floor used tapered shims behind the casing to fill the gaps. Should I cut the casing to the correct size and do a prefit to measure the thickness of the shims required or should I just build the shims and install them before cutting the casing? I want to be sure that I get a good fit on the miters am unsure which method would provide the best results.
I have read in previous posts where suggestions were made to outline the casing with a pencil and then beat the sheetrock with a hammer to crush it to eliminate the gap. Since this would create a compound miter cut, I am somewhat hesitant in doing this as I mentioned, I want a good fit on the miters and feel that doing this method would not produce the results that I desire.
Also, when making a tapered shim on the tablesaw, what is the best method for acheiving this as my windows are 65" tall and making a tapered shim 65" long is something I am not exactly sure how to do. The shims would vary in thickness from 3/8" to 0" and everything in between so making a common shim is not an option.
Any ideas on how to proceed?
