Replacing Window Glass

Usually you can replace glass while the sash is still in the frame, but it is easier to remove the frame first and work on a table. While wearing protective clothing, wiggle and pull out the shards of glass. You may need to tap the glass with a hammer to create a new break line first.

Take care to remove all pieces of glass, putty, and metal glazing points. You may need to use a pull-type paint scraper or an old chisel. If you use a hammer, tap gently. The grooves where the new window will go must be completely smooth. A heat gun can help soften the old putty.

Wire-brush the frame and vacuum or wipe with a slightly damp rag. Apply a coat of linseed oil to the rabbet; this helps the putty stick securely.

Carefully measure the height and width of the opening in at least two places. Order a piece of glass 1/8 inch shorter in each direction. Test-fit the pane before proceeding.

Roll a ball of glazing compound into a thin rope. Press it into the corner of the rabbet. Then use a putty knife to press it firmly into place, making a thin bed of putty for the glass to rest against.

Gently press the glass into the putty bed, checking that it lies flat against the rabbet in all places. Every 6 inches or so, press a glazing point into the wood; push only gently against the glass as you go.

Roll a rope of putty about 3/4 inch thick. Aim for a fairly uniform diameter, but it need not be perfect.

Press the rope against the glass and the frame, using your thumb. Using a rag to periodically apply linseed oil to a glazier's knife or putty knife, press again using swiping motions every inch or two.

Working in the same direction and holding the knife at the correct angle so the putty will not be visible inside, press firmly and draw the knife along the line to smooth the putty.

If the resulting putty has a series of slight ridges, smooth them by lightly wiping with your finger, working in the opposite direction as in step 9.

Use a putty knife or small flat pry bar to remove the vinyl stop. Work carefully, to avoid cracking the stop. Remove the glass and order a new piece to fit.

Test to see that the new pane will fit. Scrape away the old sealing tape and clean the surface with paint thinner. Cut pieces of sealing tape to fit precisely and press them into place on the rabbet. Just before installing the glass, spread a bead of silicone sealant onto the rabbet.

Carefully set the pane in place -- you cannot adjust its position once it is set into the tape. Press the vinyl stop back into the frame to secure the glass.