Check the wood for rot. If it feels spongy or crumbles, you’ll need a wood hardener or epoxy filler before proceeding. A soft frame will just crack your new putty later.
This is a comprehensive guide to repairing window putty (also known as glazing putty). This is a manageable DIY project that saves energy and restores the look of your windows. window putty repair
The glass is cracked, the sash is rotted through, the window is second-story or higher, or you have 20+ windows to do. Professional glaziers can also remove and reset an entire pane in minutes. Check the wood for rot