Reglazing a wooden sash window with linseed oil putty is a classic DIY skill that's well within reach of a careful homeowner. Done properly, a good putty job will last decades, keeping your home weathertight and your heritage joinery looking its best. Here's how to do it right, from removing the old putty through to painting the finished bead.
Tools and Materials You'll Need
Gather everything before you start so the job goes smoothly:
- Linseed oil putty (traditional glazing putty, available at Mitre 10 or Bunnings)
- Hacking knife or old wood chisel
- Hammer
- Glazier's hacking knife or putty knife
- Stiff-bristled brush
- Glazier's sprigs (small flat-sided nails that hold the glass in place)
- Replacement glass cut to size
- Raw linseed oil
- Primer (oil-based, suitable for bare timber)
- Safety glasses and heavy leather gloves
- Tape measure and glass cutter (if cutting your own glass)
Safety note: Broken glass is extremely sharp. Always wear heavy gloves and safety glasses when removing old glass or handling new panes. Dispose of broken glass wrapped in newspaper inside a cardboard box — never loose in a rubbish bag.
Step 1 — Remove the Sash and Old Glazing
Where possible, remove the sash from the window frame before you start. Lay it flat on a padded workbench or a couple of old blankets on the ground. Working flat makes the job much easier and safer.
Using your hacking knife and hammer, carefully chip away the old hardened putty. Work at a low angle to avoid splitting the timber rebate. Once the putty is cleared, pull out the old glazier's sprigs with pliers. Lift out the broken or old glass carefully.
Clean the rebate thoroughly with a stiff brush to remove all dust and loose material.
Step 2 — Prepare the Rebate
This step is critical and often skipped — prime the bare timber rebate with an oil-based primer before applying new putty. Unprimed timber will suck the oil out of the putty, causing it to dry out and crack prematurely. Allow the primer to dry fully before continuing.
If the rebate is very dry or weathered, you can also brush on a little raw linseed oil and allow it to soak in for an hour before priming.
Step 3 — Bed the Glass
Knead your linseed oil putty until it is smooth and pliable — it should feel like soft plasticine with no cracks. If it's too stiff, work in a few drops of raw linseed oil.
Press a thin, even bedding layer of putty (about 3 mm thick) into the rebate all the way around. This cushions the glass and creates a weathertight seal at the back.
Carefully press the new glass pane into the bedding putty, pressing firmly around the edges (never the centre) until the glass sits evenly with about 1–2 mm of putty visible from the front. The glass should sit centrally in the rebate with an even gap on all sides.
Step 4 — Fix the Sprigs
Tap glazier's sprigs into the timber rebate every 150–200 mm around the pane, using the flat of your hacking knife or a small hammer. The sprigs should lie flat against the glass and sit just below the surface of the finished putty line. These hold the glass firmly in place while the putty cures.
Step 5 — Apply the Face Putty
Roll a sausage of putty and press it firmly into the angle between the glass and the rebate. Using your putty knife held at roughly 45°, draw it smoothly along each side in one continuous stroke to form a neat mitred bevel. The putty should sit flush with or just below the sight line of the rebate on the inside, so it won't be visible from indoors.
Neat mitred corners take a little practice — use a damp finger or the tip of your knife to tidy them up.
Remove any excess putty from the glass face with a clean rag dampened with a little white spirit.
Step 6 — Allow to Cure, Then Paint
Linseed oil putty needs time to form a skin before painting — typically 2 to 4 weeks in normal NZ conditions, though this varies with temperature and humidity. Painting too soon traps solvents and causes the putty to crack.
Once a firm skin has formed, apply a coat of oil-based primer over the putty, lapping slightly onto the glass (about 2 mm) to seal the putty-to-glass joint. Follow with your chosen topcoat. Resene and Dulux both offer suitable oil-based and waterborne alkyd primers and topcoats for exterior joinery.
Choosing the Right Glass
For most sash windows, 3 mm or 4 mm float glass is standard. If the window is in a hazardous location (beside a door, low to the floor, or in a bathroom), NZS 4223 requires safety glazing — check with your local glazier or council. Heritage homes may also have specific requirements around glass type.
When to Call a Professional
Glazing is not restricted work in New Zealand, so homeowners can legally carry out their own reglazing. However, consider calling a qualified glazier from tradedirectory.co.nz if:
- The pane is large, heavy, or awkward to handle safely
- The window is at height and requires a ladder or scaffolding
- The glass is in a safety glazing zone (as defined by NZS 4223) and you're unsure of the correct specification
- The sash timber is rotten and needs repair before reglazing
- You're working on a heritage or character property where council or Heritage NZ requirements may apply
For work at height, always follow WorkSafe NZ guidelines — falls from ladders are a leading cause of serious DIY injuries.
Window & Glass Association
