How to Replace Sash Window Putty

Glazing putty protects the edge of a pane and helps shed water. Cracked or missing putty should be assessed before water reaches the rebate.

Safety first

Old glass can be thin and brittle. Avoid heat near historic glazing and consider the possibility of lead-containing paint.

Repair principles

Suitable putty must be compatible with the glass, timber preparation and paint system. Retain historic glass where practical and have damaged or unsafe glazing assessed by a competent glazier.

What glazing putty does

Traditional putty beds and seals glass at the rebate, helping shed water and protect the timber beneath. When it cracks or detaches, moisture may enter the joint.

Inspect the pane

Look for loose glass, missing sprigs or points, cracked putty and softened surrounding timber. Historic glass may have ripples and slight distortion worth preserving.

Compatibility matters

Putty, primer and paint systems need to work together. Some modern glazing products are not suitable for all traditional details or coated glass, so follow the manufacturer’s instructions.

Avoid risky removal methods

Aggressive scraping and high heat can break fragile glass, damage narrow glazing bars or disturb old lead-containing coatings. Broken or loose panes should be handled by a competent glazier.

Finishing and maintenance

Proper preparation and paint overlap at the glass edge help weather protection. Reinspect the window after seasonal movement and address any early cracks before water reaches the rebate.