Broken window glass can be replaced with regular glass or plastic unbreakable glass, usually acrylic. Before starting to replace broken glass, put on a pair of gloves and a pair of glasses. It is easy for bits of glass to chip and fly. Glass, in both wood and metal frames, is normally held in place by a mechanical fastener. In wooden windows, these are usually glazers points, a small triangle of thin metal. In metal spring clips are used. A glazing putty or glazing compound is then applied to hold the glass in place and seal it from the weather and the rain. The following steps are suggested for replacing broken window glass:
Carefully remove all pieces of glass being careful to clean up the area around the window to prevent injury and cuts. Use pliers to grip pieces of glass still in the window.
With a chisel or utility knife, remove the old putty. Be careful not to gouge the wood frame. As you proceed around the frame you will find glazier points (small steel triangles) in wood frames or spring clips in metal window frames. Save the points or clips. Be sure all old putty is removed so the glass will slide into place easily.
With sandpaper or a scraper, clean off bits of putty which remain on the wood or metal sash.
Paint the frame with an oil-based wood preservative or an oil-based primer. This seals the wood surface under the putty and prevents the metal frame from rusting. A fast-drying primer is the most convenient.
Measure the size of the glass with a measuring tape allowing 1/8" clearance on all sides by reducing each measured dimension by 1/4". Buy the glass cut to the correct size.
Knead the glazing compound to get it really soft and malleable and apply a thin ribbon of it in the glass recess of the window frame. Keep the thickness of this glazing compound fairly uniform so when you press the glass down into the compound it will not crack. Install the glass, pressing it firmly into the glazing compound, and insert the glazier points (small metal triangles) in place to secure the glass pane. Push these in with a large screwdriver or a putty knife. If you use a hammer be careful not to break the glass. The points should be placed every 6" to 8". The spring clips for metal windows should be inserted in the slots provided in the steel frame.
Knead the glazing compound and form it into strings no bigger than a pencil. Lay a string of putty along one side at a time and force it onto the glass and wood frame with the tip of a putty knife. Smudges from the compound can be removed later with a cloth dipped in mineral spirits or turpentine.
After the glazing compound has dried, paint it to finish sealing the seams between the glass and the compound, and the wood and the compound.