Crack! An errant baseball, a hurled stone, or a falling branch is all it takes to end the life of a windowpane. And for most modern, double-glazed windows, that means a trip to the local glass shop for repairs.

But for old-fashioned, single-glazed wood sash, you can easily replace the pane yourself. It's one of the rare homeowner projects that doesn't require some practice to tool the putty," says Tom Silva, This Old House general contractor. "You want to end up with neat, crisp creases in the corners and straight runs in between."

The reglazing technique Tom demonstrates on these pages also comes in handy when the old putty itself cracks or falls out but the glass remains intact. (In that case, Tom removes all the old putty; it's too far gone to patch.) Whatever the glazing project, he recommends taking out the window sash and laying it flat on a workbench, if possible. "Trying to reglaze a sash that's still in it's opening takes longer, and it's far more difficult to do a good job."
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    Tools List

    • putty knife
      ½-inch putty knife,
      For tooling putty; should be flexible and clean.
    • painter's tool
      5-in-1 Painter's tool,
      For scraping out old putty.
    • electric heat gun
      Heat gun,
      For softening old putty.
    • paintbrush
      1-inch paint brush,
      For priming sash.

    Shopping List

    1. GLASS
    For pane dimensions, measure the opening from top to bottom and side to side, then subtract 1/8 inch from each measurement.

    Protects undamaged glass from heat.

    Hold glass against sash. Tom uses push-type points with shoulders.

    Seals the edge of the glass against the weather. Tom uses an oil-based product in a can.

    Seals wood against moisture; extends putty life.