How to Cut and Replace Broken Glass

Scrape and pry out the putty from the window pane with your painter's multi-tool. Take your time, being careful not to gouge the soft wood. If you encounter hardened putty that won’t come loose by scraping, use a heat gun to soften the stubborn glazing and then try scraping again. Lightly sand the wood, making sure that it is clean and the groove is clear of debris. You can use a small brush to sweep any debris away from the surface. Pull out the old glazing points with pliers. This will avoid snagging them when sanding the wood.

With your surface cleaned, it is time to place the new pane of glass into the empty space. Measure the opening and then subtract 1/8 inch to ensure the new glass will fit. Use new glazing points to hold the glass in place.

If you are using oil-based putty, begin to knead it to soften it up. There are two main ways to apply oil-based glaze. The first is the “snake,” where the putty is rolled into a long thin length for application. The second way to use an egg-sized piece of putty that is kneaded and then applied piece-by-piece with your putty knife to press against the glass. Latex glaze is easier to apply using a caulk gun or putty knife.

Lay a small bead of putty on the inside of the pane and press the glass into place. Any overflow on the inside can be trimmed away later after drying. Place new glazing points into the sides to hold the new pane in place. Caulk the front of the pane, making sure to apply a healthy bead of glaze. Using a caulk tool, smooth out the glaze and remove any excess.

For oil-based glaze, apply a thick layer of the putty. As with the latex, don’t leave any gaps or recessed areas. Smooth the putty out by applying mineral spirits to the putty knife and running it over the surface until it is complete. Pull any excess putty away from the smooth joint edge and scrape it away.

Allow the putty time to dry before any sanding or painting. Latex glaze should dry within 12-24 hours, oil-based may take a week to 15 days to fully cure. When painting the compound, it is okay to allow a little paint to flow onto the glass to help add a weather-tight seal.

Clean the side you want to cut with glass cleaner and a microfiber cloth to remove and grit and oils. Clean glass helps to make a smoother cut. With a tape measure or ruler, measure out your intended cut line and mark with several dots. Using a straight edge and a wax pencil or permanent marker, connect the dots to make a straight cutting line.

Score the glass along your cutting line with the glass cutter. Press down firmly and slowly pull the cutter towards you along your mark. Maintain even pressure to ensure a true scoring of the glass. Try to make the cut in one smooth action, as stopping and starting again may not make an even cut. Listen for a ripping sound as you are cutting as this will indicate a clean cut.

After you have made a complete pass along the cut line, turn the glass over and snap along the line with gentle pressure. You can sand down the rough edges with 400-grit sandpaper.