ask This Old House
The broken panes in my old wood windows need replacing, but the caulk is rock hard and stuck solid to the sash. Any helpful hints?
—WAYNE EDSFORTH, GREENWICH, NY
TOH GENERAL CONTRACTOR TOM SILVA REPLIES: That caulk, called glazing putty, has long been used by wood-window-makers and restorers to seal glass to the sash. When putty is fresh, it’s soft and easy to tool, but after 30 or 40 years it gets brittle and crumbly and no longer provides an effective barrier against water and air.
Removing old putty is the most time-consuming part of any window re-glazing project; it has to be done carefully to avoid damaging the sash or your health. Old putties may contain asbestos or be covered with lead paint, so be sure to wear safety glasses and a dual-cartridge, NIOSH approved P100 respirator, and to use a vacuum with a HEPA filter.
If you can’t cut away the putty with a utility knife, try softening it with an infrared heater or heat gun fitted with a shielded nozzle, then scrape it off with a putty knife. Protect the other panes from the heat with doubled sheets of aluminum foil.
But if your windows have a cement based putty from the 1920s and ’30s, which is impervious to heat, shave it off using multiple passes with an old “beater” chisel. Clear the glass first, then turn the edge of the blade upright and shave the remaining putty off the sash.
The next steps are the same for any window. Pry out the metal glazier’s points, lift out the broken glass,
