Metal windows are often sealed with rubber gaskets instead of putty, but some have both, and when you need to replace a cloudy or broken pane, you have to take out the old putty. The main complication in this otherwise straightforward task is that old putty is often so hard that you cannot cut it or work a putty knife beneath it. You can use one of two methods to soften the putty to make it easier to pry out, but if you are in a hurry, you may prefer to fit a putty-grinding attachment to your drill instead.
1 Work the edge of a putty knife behind the putty in the middle of one of the edges of the frame. Twist the knife to chip and break the putty. It helps if the knife has a sharp edge. An easy way to sharpen the edge is to hold it against a belt sander with a 100-grit belt.
2 Mix equal parts of boiled linseed oil and household chlorine bleach and brush the mixture onto the putty to soften it and make it easier to remove. Let the mixture soak in for 30 minutes before scraping. The mixture does not work as well if the putty is covered with paint.
3 Heat the putty with a heat gun as an alternative method to soften it. Hold the gun about 3 inches from the putty -- being careful to angle it away from the glass -- and let the heat penetrate until the putty is soft enough to remove, which typically takes from 5 to 10 seconds.
4 Grind the putty with a specialty tool that fits in your electric or battery drill. The tool has a carbide bit and a plastic handle that allows you to grind out the old putty quickly without damaging the window or the frame.
5 Insert the grinder into your drill, start the drill and run the tip carefully along one edge of the frame. Hold the tip steady by gripping the plastic handle with your free hand. After you are done grinding, chip out any residue that remains with a putty knife.