This week’s Ask The Craftsman question comes from Mike.
“When reglazing windows, do you have to remove all the old putty or will new putty bond to the old putty?”
Mike, it can be a real chore removing every ounce of old putty when you restore a window and the truth is that not every little bit has be taken out.
You can patch in new putty on top of old putty as long as the old stuff is still adhering well.
We call this spot glazing and here’s how you do it:
Using a putty knife or 5-in-1, dig out as much of the old putty as possible. Leave the really stubborn stuff in place. Blow off any remaining dust after you’re done, then wipe the surface with a little bit of Boiled Linseed Oil and apply your new putty. Clean off the excess oil from the glass with a little whiting and you’re done.
The real challenge is keeping your new putty lines from being too big that they are visible from the window’s interior. This won’t cause any performance issues, but big fat putty beds aren’t very attractive.
Don’t forget to paint your fresh putty as soon as it develops a skin.
Good luck with the windows!