After having new French doors installed there is a gap which has been left which is approx 12inches long, 2 inches wide and 2 inches deep. After asking the installer to come back and fix it several times I have decided to do it myself. Can you please advise me the best filler to use.
if there is a gap between the frame and the wall, then use expanding foam, leave it to set and then cut the excess off. You can cover the gap later with a plastic trim, that you can buy from your local plastic suppliers