Glass windows let you see the world around you while keeping out the heat, the cold, insects and wind. However, glass is breakable, and an errant baseball or hailstorm can leave you with a broken pane of glass. When this happens, your window can let in the cold, the heat or the rain. In addition, a broken window can be a safety hazard. The best approach for fixing a broken window is to replace the entire pane of glass.
Don safety goggles and heavy work gloves when working with glass. Cover the area under the window on both sides as well as surrounding panes with newspaper to protect the areas from broken glass and make cleanup easier.
Carefully remove all pieces of broken glass, and dispose of them in a trash can. If necessary, use a wet/dry vacuum to get out the small shards; make sure you empty the vacuum immediately after you finish this project to ensure that no one else uses it with the glass in there.
Scrape away all glue, glazing, putty and other contaminants from the mullions, or pieces of wood, surrounding the pane. Any paint pieces or debris prevent the pane from sitting level. If any of the putty is too stiff to scrape away, soften the material with a heat gun or soak it with linseed oil, and scrape again. Continue until all debris is gone.
Pry out any old glazing points from the window frame with needle-nose pliers. These points are small metal pieces that help hold the glass steady in the frame. You will add new ones later.
Wipe down the wood with a rag dampened in mineral spirits to remove any residual dirt and dust. Lightly sand the wood with fine-grit sandpaper, and paint on a thin layer of wood sealant to help protect the new glass from moisture. Allow the sealant to dry completely before continuing.
Spread a rope of adhesive putty around the exterior of the mullion with a putty knife. Flatten it as much as possible against the mullion, and make sure you get a smooth, even layer so that the pane sits flat.
Set the pane of glass in place over the putty so that it rests against the tabs of the surrounding mullions. When the pane is completely flat, drive the glazing points into the surrounding frame with the flat edge of your putty knife, installing a point every 4 to 6 inches along the pane to help secure it in place.
Recoat the edges of the pane and frame with putty or sealing glaze, again working in a thin layer to create a flat seal. Scrape away any excess with the putty knife. When the top layer dries, paint it to match the frame to help the repair blend in.