How to Replace a Pane of Glass in a Window

The need to replace a pane of glass can pop up for any number of reasons. A window pane could be broken by the proverbial errant baseball or you could decide to upgrade to a newer type of glass. No matter the reason, replacing the glass is an easy task once you understand the steps and process.

Removing the putty used to be the the hardest part of replacing a pane of glass, but there are ways of making the job easier. Brush the old putty with a coat of lacquer paint thinner and let it set for 15 minutes. The thinner will penetrate the old putty to effectively break its seal. Afterward, scrape the off the old material with a putty knife.

When the sash wood is clean and free of putty and the glass shards have been removed, measure the inside depression where the glass rests from top to bottom and side to side. The glass should be cut 1/8 inch smaller than the measured dimensions of the sash frame for a flawless fit.

To cut a piece of glass to the proper dimensions, lay the glass on a clean, flat surface. Measure off the dimensions and use a felt-tip marker or crayon for reference. Lay a straightedge between two of the reference points and score the glass with a glass cutter.

A glass cutter is a pencil-like tool equipped with an extremely sharp metal wheel that is hard enough to scratch glass. Hold the tool between the index and middle finger and, with firm steady pressure, run it along the straightedge to cut the glass. Do not go over the scratch line. If there are portions along the line where no scratch occurred, go over just these parts.

Lay the scored piece of glass over the edge of a table so that the scored line is even with the edge. Hold the measured piece firmly onto the table's surface and push down with a quick, sharp motion on the unsupported waste piece. It should break off cleanly along the scored line. If their exists some irregular breaks in the edge of the glass, use the jaws of combination pliers to break them off.

Coat the edges of the sash frame depression with linseed oil or paint to prevent the absorption of the glazing putty oil in the wood of the frame. Lay a small bead of of glazing compound on the edge of the depression on which the new glass pane will rest. Place the glass into the sash frame and onto the compound. Press it firmly along the edges to ensure that it is well seated.

Glazing points are used to hold the glass securely in place. Using a flat-tip screwdriver, push the points into the sash frame approximately 6 inches apart. The points have shoulders to accommodate the tip of the screwdriver and should be pressed into the wood until the shoulders are flush with the surface.

Roll some putty into a snake-like form and press it into a corner. Continue around the perimeter and then make smooth using a putty knife. The angle at which the knife is held determines the angle of the putty. If the angle is too shallow, the putty will extend into the glass to far and be visible from the inside.

After the putty has dried for a week, it can be painted. Allow the paint to overlap onto the glass at least 1/16 inch to seal it against rain. Hardware stores and home centers carry all the necessary tools and materials necessary to complete the job successfully.

Always work safely.