How to Replace a Broken Pane in a Historic Window (Without Ruining the Sash)
Replacing a broken window pane in a historic sash isn’t just a quick fix—it’s a delicate surgery. Do it wrong, and you could damage century-old wood, destroy irreplaceable wavy glass, or end up with a drafty, leaky mess. Do it right, and you preserve a beautiful, functional piece of history that’s good for another generation (or two).
Whether you’re a DIY weekend warrior or just want to understand how the pros at Austin Historical do it, here’s your step-by-step guide to replacing a single pane the old-fashioned (and right) way.
Step 1: Know What You’re Working With
Before you touch anything, figure out what type of glass and sash you have.
Is it wavy glass? That’s likely original and needs extra care.
Old-growth wood sash? You want to preserve as much of that as possible.
Glazing type? Linseed oil putty is traditional; caulk is not.
If you're in a historic district, double-check local regulations before replacing original materials.
Step 2: Safety First
Wear gloves, eye protection, and consider a dust mask—especially if lead paint is present.
Lay down a padded surface to work on the sash safely.
If the glass is cracked but intact, apply painter’s tape over it to reduce shattering during removal.
Step 3: Remove the Broken Glass and Old Putty
Use a glazing tool, utility knife, or steam to soften and remove old glazing putty.
Carefully remove the glazier’s points (the small metal triangles holding the glass).
Gently lift out the broken pane. If it shatters, remove shards with pliers and vacuum thoroughly.
Pro tip: Never use heat guns on antique glass—thermal shock can crack adjacent panes.
Step 4: Clean and Prepare the Rabbet
Scrape and sand the glazing bed (the channel where the glass sits).
Apply a thin coat of boiled linseed oil to condition dry wood—this helps the new putty adhere and prevents oil absorption from the compound.
Step 5: Bed the New Glass
Apply a thin layer of putty in the channel. (We recommend Austin’s Glazier Putty)
Gently press the new glass into the soft putty so it beds evenly.
Use glazier’s points to secure the pane (usually 2 per side).
Step 6: Apply Finish Glazing Compound
Roll putty into thin ropes and press it along the edge of the glass.
Tool it to a clean 45-degree bevel with a putty knife.
Clean off excess putty and let it cure (usually 7–14 days, depending on the product).
Step 7: Paint to Seal the Deal Once the putty skins over and firms up, paint it with oil- or latex-based paint—extending the paint line just slightly onto the glass for a proper weather seal.
Glass Selection Tips
Restoration glass is available to match original wavy or seeded textures.
Don’t use modern double-pane glass—it won’t fit historic sashes.
Laminated or tempered glass can be used in specific safety applications but may require frame reinforcement.
Common Mistakes to Avoid
Using caulk instead of putty
Over-tightening or under-using glazier’s points
Forgetting to seal the putty with paint
Rushing the job—putty needs proper cure time
When to Call the Pros
If you’re dealing with:
Original cylinder or crown glass
Severely rotted sash or muntins
Lead paint remediation
High window locations or heavy storms
…then it’s time to call Austin Historical. We do this daily, and we do it right.
Final Word
Replacing a broken window pane doesn’t have to be intimidating. With the right tools, materials, and techniques, you can extend the life of your historic windows while preserving their soul. Take your time, respect the craftsmanship, and remember: sometimes the smallest pane holds the biggest piece of history.
