The most important thing to remember when you install new window glass is the correct thickness of glass to buy. Small windows normally need only 1/8-inch-thick glass, but ¼-inch-thickness is more common in larger windows and doors. If the pane was frosted or patterned, take a small sample of the broken glass to your supplier so you can get an exact match.
To install new window glass, you will need:
- tape measure
- putty knife
- dry powdered filler
- glazing points
1. Measure the exact width and height of the opening, taking the measurement right up to the muntins. Then deduct 1/8-inch from each dimension to allow for the putty that will be embedded around the glass and to reduce any risk of future cracks caused by minor expansion and contraction. Measure from corner to corner on each side in case the window isn’t square.
2. Coat your hands with a small amount of dry powdered filler before you handle the putty to soak up excess oil and make mixing a bit easier. Take a large amount of putty and work it in your hands. This ensures that the oil and any small lumps are mixed together into a smooth pliable ball.
3. Roll the putty into thin ropes and firmly press them into and around all four sides of the window opening.
4. Carefully place the new pane of glass into the opening, letting the edges of the glass embed themselves into the center of the ropes of putty. Gently press the glass in place by applying pressure at all four corners and along the edges of the pane. Never apply pressure to the center of the pane; it might break.
5. Tap a glazing point into the center of each muntin. They will hold the glass in place while the putty dries and in later years if the putty decays. Don’t set the point directly against the glass; You might crack it. Rest a piece of cardboard against the glass to avoid scratching or breaking it.
6. Mold more putty into long ropes. While they’re still pliable and relatively easy to shape, carefully press them in place over the edges of the glass and up to the muntins.
7. Use a putty knife to smooth the putty into lace. The knife is designed to produce a straight, precise line on the glass surface. Save excess putty to reuse.
8. Trim excess putty from the inside of the glass using the sharp edge of the putty knife. Let the putty dry for at least two weeks, depending on the weather, before priming and painting.
For New Panes and Glazing Beads:
When replacing an old window pane on a window that uses glazing beads, measure for the glass as shown in step 1, but use a silicone sealant to embed the pane of glass into the window frame. Once they're in securely back in place with glazing points, the wooden beads will hold the glass in position.