Removing old, cracked putty from a wooden window frame is a satisfying DIY job that most homeowners can tackle themselves. Done properly, it prepares the frame for fresh glazing putty or a new pane of glass, helping to keep your home weathertight and draught-free — important in New Zealand's varied climate, from the damp Northland winters to the cold southerlies in Otago and Southland.
Why Old Putty Needs to Come Out
Over time, linseed-oil-based glazing putty dries out, shrinks, and cracks. Once it fails, water can get behind the glass and into the timber rebate, leading to rot, mould, and eventually a loose or broken pane. Replacing failing putty is one of the simplest ways to extend the life of a wooden-framed window and keep your home compliant with the NZ Building Code's weathertightness requirements (Clause E2). BRANZ has good guidance on maintaining timber windows and preventing moisture ingress.
Tools and Materials You'll Need
- Hacking knife (a stiff-bladed putty knife) or a glazier's chisel
- Heat gun or hot-air stripper (optional but very helpful for stubborn putty)
- Hammer (for tapping the chisel)
- Needle-nose pliers (for removing old glazing sprigs or points)
- Wire brush or coarse sandpaper (80–120 grit)
- Timber primer (for bare wood)
- Safety glasses and heavy work gloves
- Drop cloth or old sheet to catch debris
Step-by-Step: Removing the Old Putty
1. Protect Yourself and the Area
Put on safety glasses and gloves before you start — old putty can chip off sharply. Lay a drop cloth on the sill and floor below to catch fragments. If the window is above ground level, make sure your ladder is stable and on firm ground.
Important safety note: Homes built before the 1980s may have putty containing lead-based paint. If you suspect lead paint (common in pre-1980 NZ homes), do not sand or grind dry — wet the surface first to suppress dust, wear a P2 respirator, and dispose of waste carefully. Check WorkSafe NZ for guidance on working safely with lead paint.
2. Soften the Putty (If Needed)
If the putty is very hard and brittle, a heat gun set to a low or medium setting can soften it enough to lift away cleanly without damaging the timber. Keep the heat gun moving — don't hold it in one spot, as you can crack the glass or scorch the wood. Work in small sections of 150–200 mm at a time.
3. Cut and Lever Out the Putty
Using your hacking knife or glazier's chisel, hold the blade at roughly a 30–45° angle to the rebate and push or tap it under the putty. Work along the length of each side, levering the putty away from the timber. Try to avoid digging the blade into the wood — you want to follow the line of the rebate.
For corners, a narrower chisel or even an old screwdriver can help get into tight spots.
4. Remove Old Glazing Sprigs
Once the putty is cleared, you'll likely find small glazing sprigs (tiny cut nails or metal points) that held the glass in place. Use needle-nose pliers to pull these out carefully. If you're reusing the same glass, handle it with care and store it flat.
5. Clean Up the Rebate
Use a wire brush or coarse sandpaper to remove any remaining putty crumbs and loose paint from the rebate. The timber surface should be clean and sound. Check for any soft or rotten wood — if you find rot, it will need to be treated or repaired before reglazing. A timber hardener product (available at most hardware stores) can stabilise minor rot.
6. Prime the Bare Timber
This step is often skipped but is really important. Bare timber will suck the oils out of fresh putty, causing it to dry out and crack prematurely. Apply a coat of timber primer to the rebate and let it dry fully before applying new putty. Resene and Dulux both offer suitable timber primers — check the product label to confirm suitability for window rebates.
Tips for a Clean Result
| Situation | Recommended Approach |
|---|---|
| Soft, recent putty | Hacking knife alone, no heat needed |
| Hard, old putty | Heat gun to soften, then chisel |
| Suspected lead paint | Wet method, P2 respirator, careful disposal |
| Rotted timber rebate | Repair rot before reglazing |
| Multiple windows | Work methodically, prime as you go |
- Work on a dry day — moisture in the timber will affect how well new putty bonds.
- Don't rush the priming step.
- If the glass is cracked or broken, remove it carefully using thick gloves and wrap fragments in newspaper before disposal.
When to Call a Professional
While removing putty is generally DIY-friendly, there are situations where it's worth calling a qualified glazier:
- The glass pane is cracked, broken, or needs replacing — handling and cutting glass carries real injury risk.
- The window frame itself is rotten or structurally compromised.
- You're working at height (above a single storey) where fall risk increases.
- The windows are heritage or heritage-listed, where specialist knowledge is needed.
- You're dealing with double-glazed units — these are factory-sealed and cannot be re-puttied in the traditional sense; a glazier will need to replace the sealed unit.
A skilled glazier can also advise whether it's worth repairing older single-glazed windows or upgrading to double glazing for better energy efficiency — something Energywise recommends for NZ homes. You can find qualified local glaziers on tradedirectory.co.nz.