I've always understood, for cleaning up mortises, and other fine tuned cuts
, one uses a paring chisel. They are supposed to be kept razor sharp, so
as to use your muscle/hand pushing to do the cutting, not by striking with
a mallet. Roy Underwood uses paring chisels, for these kinds of cuts and
clean-ups, and often notes not to use a mallet. They should be sharp enou
gh to cut with hand-pressure force.
I have several paring chisels and use them fairly often. From experience,
for these kinds of cuts, a paring chisel can't be beat.
Check Ebay for Sheffield, Addis, Sorby, or Marples paring chisels and compa
re pricing against other purchasing options. *I like old tools. Some year
s ago, I bought 1/4", 3/8", 1/2" & 1" original Robert Sorby's for about $50