It’s easier to scrape off dried paint and putty with a razor blade later than to try and be perfectly tidy while the putty is wet.

Cracked window putty isn't just an eyesore; it’s a sign that your window’s seal is failing, which can lead to wood rot, water leaks, and energy loss. Whether you have historic timber frames or standard metal ones, repairing the glazing is a manageable DIY project that can extend the life of your windows by 10 to 15 years.

Cracked window putty (glazing putty) compromises the weather seal of a window, leading to drafts, moisture intrusion, and potential rot of the window sash. This report outlines the method for repairing minor cracks and the complete process for replacing severely deteriorated putty. The repair extends the lifespan of the window and improves energy efficiency.

If you discover soft, crumbly wood under the putty (rot), the repair becomes a wood-restoration project. You will need to dig out the rot, apply wood hardener, and fill with epoxy putty before re-glazing. At that point, if the frame is extensively damaged, consider professional restoration or sash replacement.

Take a handful of fresh putty and knead it in your hands until it is warm, soft, and pliable. If it's too sticky, add a little whiting powder; if it's too stiff, add a drop of linseed oil. Roll it into "sausages" roughly the diameter of a pencil.