Why Window Glazing Matters: Preserving Historic Wood Windows

Many older homes still have their original wood windows. With proper maintenance, these windows can last well over a century. One of the most overlooked components of that longevity is the window glazing.

The glazing compound (often called window putty) is the material that seals the glass to the wood sash. It creates a weather-tight seal, cushions the glass, and prevents water from reaching the wood. Over time, however, exposure to sunlight, temperature changes, and moisture causes the putty to dry out, crack, and eventually separate from the glass.

From a distance, these windows may appear perfectly sound. Up close, the early warning signs become much more apparent.

The windows shown below illustrate a common example. While the paint is still largely intact, the glazing has begun to shrink and crack, leaving gaps where water can enter behind the glass.

The consequences of failed glazing include:

• Water infiltration into the wood sash
• Rot around the glass rabbets
• Loose or rattling glass panes
• Increased air leakage and drafts
• Costly repairs that could have been avoided with routine maintenance

At Henderson Custom Painting LLC, we approach glazing restoration differently than many contractors.

Our process includes:

• Carefully removing only the failed glazing while preserving the surrounding wood whenever possible.
• Priming the exposed wood with a slow-drying alkyd primer. We avoid modern latex primers in these areas because they do not provide the same level of penetration and protection.
• Re-glazing each pane with a high-quality glazing compound, properly tooled to shed water.
• Allowing the glazing to cure before applying finish coats.
• Painting the glazing with a slight overlap onto the glass (approximately 1/16"). This traditional technique seals the edge of the putty and significantly extends its service life.

Many painters simply paint over deteriorated glazing. While this may improve appearance temporarily, it does nothing to stop moisture intrusion and often leads to premature failure.

Proper glazing restoration is meticulous work, but it is one of the best investments a homeowner can make in preserving original wood windows. In many cases, restoring existing windows is both more durable and more architecturally appropriate than replacing them.

For homes with historic or high-quality wood windows, routine inspection and timely glazing repairs can add decades to the life of the original sash while maintaining the character and craftsmanship that modern replacement windows often cannot replicate.