The only time I’ve ever inadvertently broken a glass window was when I locked my brother out of the house during dessert. He was so angry he tapped on the glass until I’d let him inside. Needless to say I didn’t let him back in and he knocked until he broke it. In case I ever relive such a moment, here’s some easy tips for fixing old-fashioned single-glazed wood sash windows.
1. Remove The Glass – Wear gloves and cover the broken pan with a rag. Use a hammer to remove the pieces and wiggle any shard stuck into the putty with your (gloved) hands.
2. Pry Out Loose Putty – Use a painter’s tool to peel it away. For hard to remove putty, use a heat gun to loosen.
3. Prep The Rabbets – Pry the old metal glazing points out of the rabbets, the grooves in the sash where the glass sits. Scrape and sand them down to bare wood. Brush an exterior primer onto the bare wood so it won’t draw the oils out of the putty, then fill completely with new putty.
4. Bed The Glass – Wiggle the pan in place onto the put, adding pressure evenly with your hands.
5. Set The Points – At the center of each side of the pane, place a glazier’s point flat on the glass and fit the tip of the putty knife against the point’s raised shoulders. While applying slight downward pressure, gently rock the point from side to side until it’s seated in the wood.
6. Knead – Warm a handful of putty and roll it into a long rope about about ¾ inch in diameter.
For the rest of the steps, visit This Old House’s great tutorial with step-by-step photos that prove to be very helpful.