How to Repair Broken Window Glass

To repair your kid's soccer habit seemed harmless enough until a ball came crashing through the bedroom window. (Goal!) Having a glass repair service fix the damage can be expensive, but it's a simple and cheap do-it-yourself job, even for a first-timer. Think of glass repair as one of those little life skills you'll use time and again, especially if your kid's aim doesn't improve. Do It Yourself or Hire a Pro? You can replace the glass in a double-hung window for about a third of the cost a professional would charge. In fact, the only time we'd hire a pro for this task is when the sash is so horribly encrusted with paint that you'd all but destroy it by removing it. Also, if you need to replace an insulated window, a trained specialist may be the best bet for proper installation.

The importance of working safely around broken glass goes without saying. Wear heavy-duty work gloves and safety glasses to protect yourself from loose shards. Remove the window sash, and clamp it to a pair of sawhorses so it stays put while you work. Have a trash can nearby for pieces of glass and other debris.

Step by Step

1. Remove the broken glass. Carefully remove as much of the broken glass as you can with your hands. You can use pliers to remove small, stubborn shards. Wrap the broken glass in newspaper and tape it shut before putting it out with the trash.

2. Remove the glazing compound. There are a couple of ways to remove glazing compound also known as putty from the rabbet, the recessed ledge in the window sash on which the glass pane sits. You can try prying it off the sash with a scraper or a stiff putty knife, but the putty will probably be too hard. Taking care not to gouge the wood, you also can try using an old chisel to remove the compound from the window. Beforehand, score the compound by running a utility knife along a metal straightedge where the compound meets the wood. Keep in mind, though, that wood is softer than hardened putty and easily damaged by an errant scrape from a sharp knife. You may find it helpful to soften the putty with a heat gun (professional glaziers use expensive heating irons), but be careful too much heat may damage the wood and create more repair work.

3. Remove the glazing points. Once you've removed the old glazing compound, use long-nosed pliers to pull the glazing points and any other debris from the rabbet.

4. Measure for replacement glass. Once you've cleaned the area, measure the distances between the top and bottom rabbets and the two side rabbets. Subtract 1/8 inch from both measurements to determine the height and width of the new glass pane. Order glass cut to fit at a glass or hardware store. For most windows larger than about 2 feet by 2 feet, order double-strength window glass.

5. Prime the rabbet. Apply an exterior-grade primer to the rabbet. The primer prevents the wood from absorbing the oil in the glazing compound and drying it out. Allow four to six hours for a latex primer to dry before continuing; let an oil-based primer dry overnight. Quick-drying primers are a great convenience for small projects like this.

6. Install the new glass pane. Apply a 1/8-inch bead of glazing compound or acrylic caulk around the rabbet's perimeter, and press the glass pane into place to create a tight seal. Install glazing points at 8-inch intervals around the glass. Press the tip of the glazing point into the side of the rabbet, and use a stiff putty knife or a screwdriver to wiggle the point into the wood, as shown in the animation.

7. Apply a fresh glazing compound. Massage the compound to make it warm and pliable, and roll it between your hands to form a rope that's about 3/8 inch in diameter. With your fingers, press the compound into the rabbet where the edge of the glass meets the window sash. Use a putty knife to smooth the compound: Hold the knife at about a 60-degree angle, sloping away from the glass. Starting at one corner, drag the knife along the compound, molding it into a neat, uniform bevel as you go. Touch up the corners at the end, and remove any putty you've trimmed off.

Tip from the pros on fixing your broken window:

A rag dipped in turpentine will help remove any smudges left on the glass. Wait a day or two before cleaning smudges, however, so you don't disturb the newly set compound. Also, dipping your putty knife in turpentine will help smooth the surface of the compound as you press it into place.8. Prime and paint. When the putty has formed a skin a process that can take weeks to apply a coat of exterior primer over it. (There are as many opinions on how long to wait as there are repair people, so follow manufacturers' instructions on the putty can.) Oil-based primer bonds are best for glazing compounds. After the primer dries, apply a coat of exterior trim paint.