How to Replace Window Glazing

The glass in older, single-pane windows is surrounded by a glazing compound, also known as putty. Cracked or missing window glazing can allow serious air seepage and run up your winter heating bills quickly. Replacing the window glazing can help you save money and improve the look of your windows.

Things You'll Need

• 1 1/2 inch putty knife
• 5-in-1 painter's tool
• Heat gun
• 1-inch paint brush
• Scrap piece of metal flashing
• Aluminum foil
• Glazing putty

Instructions

Remove old glazing

1. Use a painter's tool to pry out any loose putty from the edges of the pane.

2. If any old glazing remains, you will need to remove it. Place doubled sheets of aluminum foil on any adjacent panes to protect from the heat of the heat gun.

3. Hold a piece of metal flashing against the glass pane you are working on to protect it from heat. Use a heat gun in a back and forth motion about an inch away from the remaining putty to slowly soften it. Use the painter's tool to pry the remaining glazing out once adequately softened.

4. Glazing points are the triangular flat pieces of metal that hold the pane of glass to the wood sash under the putty. Remove the old metal glazing points from the rabbets, the grooves in the sash where the glass sits. Scrape and sand the rabbets until you achieve bare wood.

Installing new glazing

1. Apply an exterior primer onto the bare wood. This prevents the wood from drawing the oils out of the putty and reducing its life. Allow the paint to dry completely.

2. Knead a handful of putty until it's warm and pliable, and press it into the rabbets. Be certain to fill them completely. You do not need to be too concerned with neatness at this stage.

3. Place a new glazing point flat on the glass, and use the tip of the putty knife against the raised shoulders or the point. Apply slight downward pressure and gently rock the point from side to side until it's seated in the wood. The glazing (or glazer's) points can be picked up at most hardware stores. Repeat the same process on the opposite corner of the pane. Space points evenly 4 to 6 inches apart, and do the same on the other side of the glass.

4. Warm up about a handful of putty. Roll it into a long rope approximately ¾ inch in diameter.

5. Position the rope around the edges of the glass, and push it firmly against the exposed rabbets. If one rope does not cover the entire sill, it is okay to roll out more and overlap the ends to form an unbroken string of putty around the edges of the glass.

6. Begin at a corner. Gently place the putty knife's blade at about a 45-degree angle to the glass. The tip of the blade should be on the top edge of the rabbet with one corner on the glass. Use your index finger to flatten the blade against the putty and keep the same angle as you pull the knife along one side of the pane. Leave a neat crease in the corner, and gather the excess putty. For the rest of the sides, put the tip of the blade on the crease and repeat the tooling process.

7. Once all excess putty is removed, wipe the putty down with mineral spirits, also known as paint thinner, to eliminate oils.

Tips & Warnings

• If your fresh glaze can be seen from the other side of the window, you will need to trim off a little more with your blade. Once you are satisfied with the appearance, allow the glazing to set for seven to 10 days. Then apply an oil-based primer followed by a quality exterior paint; each should extend onto the glass by about 1/16 of an inch to prohibit water from getting behind the glaze.

References

• This Old House
• Fixing Our Historic House
• Natural Handyman