How to Fix Broken Glass in a Window

That ill-flung baseball or confused bird always seems to find your window.

Replacing single-pane window glass

If it broke a single-pane window, you're in luck--this is usually a straightforward task, as long as the window is on a ground floor and the sash is removable.

Remove the window sash and place it flat on a worktable to remove what's left of the glass. Lay a towel over the glass to break it and carefully wiggle out the pieces.

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Remove the glazing compound on the glass perimeter. Old glazing compound may be hardened and difficult to remove, or so brittle it practically falls off. Use a glazier's tool, an old chisel or flathead screwdriver, or a putty knife to pry and scrape out the compound. Pull out any glazing points (small metal fasteners that hold the glass in place) with long-nose pliers (see A).

Brush a fast-drying paint primer on any bare wood exposed while removing the old compound. This seal prevents too-dry wood from absorbing all the glazing compound's oils.

If you need to buy glass, measure the opening it will fill, then have the store clerk cut a replacement pane 1/8 inch (3 mm) shorter and narrower than those dimensions.

If you have a piece of glass handy that requires cutting to fit, place it on a thin rug or other firm, padded surface. Lay a metal straightedge, square or ruler over the glass at the cut line and use a glass cutter to score from edge to edge with one continuous, firm stroke. Then position the scored line on the glass over the edge of a table or board. Snap the overhanging portion downward sharply to complete the cut.

For a weatherproof and watertight seal on the exterior, apply a thin bead of caulk on the frame perimeter as a setting bed before installing the glass. Alternatively, use a thin coat of glazing compound and press it into place with a putty knife.

Put the new pane in the frame, pressing just hard enough to bed it in the compound or caulk.

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Place at least two glazing points on the glass with the points facing the frame along each side, about 2 inches (5 cm) in from each corner; use additional points so the maximum span between them is 8 inches (20 cm). Press the points into the wood using a glazier's tool or putty knife (see B).

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Roll a handful of glazing compound between your hands until it is soft and pliable. Then roll it out on a flat surface to form a rope of 3/8-inch (1-cm) diameter and press it into the corner between the glass and the wood frame with your fingertips (see C).

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Use a glazier's tool or stiff putty knife to press the compound firmly into place against the glass and the wood frame (see D). Angle and cock the tool as needed so the beveled compound fills the gap but projects above the wood when viewed from inside. Finish each side with one long continuous stroke.

Scrape off any excess compound with the same tool or knife and clean the glass carefully without disturbing the compound.

Put the sash back in and allow the glazing compound to dry for a week or more.

Paint over the glazing with exterior trim paint to seal and protect it from the weather. Mask the glass with tape or liquid masking and paint it freehand. Paint about 1/8 inch (3 mm) out onto the glass to form a watertight seal (see Tips).

Scrape off any excess paint on the glass with a single-edge razor in a holder. Try to leave the thin edge of paint on the glass to maintain the seal.

Things You Will Need

  • Exterior Trim Paint
  • Glass Cleaner
  • Glazing Points
  • Small Paintbrush
  • Tape Or Liquid Masking
  • Towel
  • Single-edge Razor
  • Replacement Glass
  • Fast-drying Paint Primer
  • Glass Cutter
  • Long-nose Pliers
  • Chisel Or Flathead Screwdriver
  • Glazier's Tool Or Stiff Putty Knife
  • Glazing Compound
  • Silicone Or Siliconized Acrylic Caulk
  • Tape Measure
  • Metal straightedge, square or ruler

Tips

  • Make vertical cuts by rolling the blade of a putty knife into the joint between the sash and the glazing compound. This breaks the joint cleanly and prevents accidental damage to the sash.
  • To maintain the proper 1/8-inch (3-mm) paint seal on the glass, either use Wagner's Glass Mask, which includes a liquid masking system and special scraper (available at many paint and home centers); or hold a wide spackle knife or scraper against the wood muntin as you scrape the paint off the glass.
  • When double-pane or insulated windows break, or the seal fails and the inside surface fogs up, you may need to replace the entire sash, including the glass and the frame around it. Contact a local glass shop or window-repairing professional for advice on your specific situation.

Warning

  • Wear heavy work gloves and proper eye protection, such as goggles.