Last time we looked at how to take apart your double-hung window before you repair and paint it.
Now that you have the top and bottom sash on your bench, check out the putty. If it’s cracked or raised, it’s better to replace it rather than attempting patch-ups. It’ll give you an airtight window, and will mean less repairs down the road.
Old putty is hard and brittle. Soften it by spraying the frame with linseed oil (before removing the old paint, that is). You can also try using a soldering iron, but be careful about the effect of heat on the window pane.
Once you’ve removed the putty, look for the glazier’s points which hold the glass in place. These are small metal triangles which are inserted into the window frame. Remove these, and carefully loosen the glass.
With the glass out, strip the paint and any remaining putty. Prime the window with an oil-based primer or paint.
To replace the glass, measure the window in several places. Deduct 1/8″ from your measurements to ensure that the glass fits easily into the frame. Most local hardware stores can cut glass to measure and advise on the thickness required, but to be sure use the existing glass as a guide as to what should be replaced. Purchase putty that’s appropriate for a wood frame, pressing it into the rebate of the window.
Place the newly cut glass on the lower edge of the sash frame and gently seat the pane into place, pressing gently to ensure a seal. Glazier points may be used to secure the window, but if working horizontally this security may not be necessary. Place a final bead of putty around the perimeter of the glass press it into place, removing excess, with a putty knife. Allow about three days for the putty to dry, and you’re ready to paint.