Before you fix a broken window, you have to first remove the old glazing compound and glazier's points. If you are just replacing old, cracked glazing compound, you may leave the glazier's points in place. Either way, glazing compound must be carefully removed to avoid injury to yourself, the window frame and the window pane (if not already broken). Using a heat gun and a chisel, you can easily remove old window glaze.
Pick loose glazing compound off with your fingers if it is easily removable. Making a gap in the glaze will make it easier to heat the window frame to remove old glazing compound.
Put on safety goggles to protect your eyes from glass or other debris. Position the switch on the heat gun to its lowest temperature setting and turn it on. Hold the gun 3 inches from the glaze for a couple of seconds, then turn it off. Feel the glazing compound to see if it is softening. If not soft enough for removal, hold the gun a little closer to the window and heat the glaze again. Repeat until the glaze is soft enough for removal. You will have to do this in sections, working your way around the window frame.
Pull the old glazing compound away from the frame and window, using a chisel and triangle scraper. Be very careful to avoid damaging the frame or the window.
Extract the old glazier's points with a putty knife, if you are removing the window pane, and save them for future use. Newer glazier's points are typically larger than the old points and may not work well when replacing windows in an older frame.
Clean any residual glazing compound from the window frame with a putty knife and a triangle scraper. Use a sash paint brush to dust any debris from the window frame so the new glazing compound will adhere well.
Applying too much heat too quickly can result in glass cracking and fire.