Reglazing a steel-framed window is a manageable DIY project for most homeowners, provided the frame is in reasonable condition and the pane is a straightforward single-glazed replacement. The key differences from timber-framed windows are rust treatment and using the correct metal casement putty — standard linseed oil putty is not suitable for steel frames.
Safety First
Broken glass is extremely sharp and can cause serious cuts. Always wear heavy-duty leather gloves and safety glasses when removing old glass and putty. If the existing glass is old enough to be lead light or you suspect it may contain asbestos-based putty (possible in pre-1980s homes), stop work and seek professional advice. WorkSafe NZ has guidance on working safely with hazardous materials.
Tools and Materials You'll Need
- Hacking knife or old wood chisel
- Putty knife / glazing knife
- Wire brush and coarse sandpaper
- Rust converter or zinc-based metal primer
- Metal casement putty (specifically formulated for steel frames)
- Replacement glass cut to size (have your local glazier cut this for you)
- Spring clips / glazing clips (the small metal clips that hold glass in steel frames)
- Methylated spirits or mineral turpentine for cleaning
- Exterior metal paint to finish the putty once cured
Metal casement putty is available from glazing suppliers and hardware stores such as Bunnings or Mitre 10. Check the product label confirms it is suitable for metal frames.
Step 1 — Remove the Old Glass and Putty
Using a hacking knife or old chisel, carefully chip away the old hardened putty from the rebate (the channel the glass sits in). Work steadily around all four sides. Once the putty is loosened, remove the spring clips — note how many there are and their spacing so you can replace them correctly. Carefully lift out the broken or old glass pane.
Step 2 — Treat the Frame for Rust
This step is critical for NZ conditions, particularly in coastal areas where salt air accelerates corrosion. Use a wire brush and sandpaper to remove all loose rust and old paint from the rebate. Apply a rust converter to any active rust, following the product instructions, then prime bare metal with a zinc-based metal primer. Allow to dry fully before proceeding — skipping this step will cause new putty to fail prematurely.
Step 3 — Bed the New Glass
Roll a thin rope of metal casement putty (about 3 mm diameter) and press it firmly into the rebate all the way around — this is called the back bedding layer. It cushions the glass and creates a weathertight seal at the back.
Carefully place the new glass pane into the rebate, pressing it gently but firmly into the bedding putty. The glass should be centred with an even gap (typically 2–3 mm) on all sides — this is called the edge clearance and allows for thermal movement. Do not force the glass hard against the frame.
Step 4 — Fit the Spring Clips
Press the spring clips back into their holes in the steel frame at regular intervals (typically every 150–200 mm, or as they were originally). These clips are what physically hold the glass in place — the putty alone does not retain the glass in a steel frame. Make sure every clip is fully seated.
Step 5 — Apply the Face Putty
Take a good handful of metal casement putty and press it firmly into the angle between the glass and the frame. Using your putty knife held at a consistent 45-degree angle, draw it smoothly along each side to form a neat chamfered bead. The putty should be flush with or just below the sight line (the inner edge of the frame) so it is not visible from inside. Mitre the corners neatly with the knife.
Remove any excess putty from the glass face with a clean putty knife, then wipe the glass clean with a rag dampened with methylated spirits.
Step 6 — Allow to Cure and Paint
Metal casement putty needs time to skin over before painting — typically 5 to 7 days in normal NZ conditions, though this varies by brand and weather. Check the manufacturer's instructions. Once skinned, apply a coat of exterior metal paint over the putty and onto the glass by about 2 mm to seal the putty-to-glass junction and prevent water ingress. This paint overlap is an important weatherproofing step. Resene and Dulux both offer suitable exterior metal paints — check their technical datasheets for compatibility.
Does This Work Require a Building Consent?
Like-for-like replacement of a single pane of glass in an existing window is generally exempt from building consent under Schedule 1 of the Building Act 2004. However, if you are changing the glass type (for example, upgrading to safety glass or double glazing), or altering the frame, the rules may differ. Always confirm with your local council. You can find general guidance at MBIE Building Performance.
Note: If the window is in a Healthy Homes rental property context, there may be additional requirements around glazing and draught stopping — check Tenancy Services for the current standards.
When to Call a Professional
Call a qualified glazier if:
- The glass pane is large, unusually shaped, or in a high or difficult-to-reach location
- The steel frame is badly rusted, bent, or structurally compromised
- You need safety glass (toughened or laminated) — required by the NZ Building Code in certain locations such as near doors, low-level panels, and bathrooms
- You suspect hazardous materials (asbestos putty, lead glazing)
- You are not confident working at height
A qualified local glazier can cut glass to size, advise on the correct glass specification, and ensure the work meets NZ Building Code requirements. You can find experienced glaziers in your area on tradedirectory.co.nz.
Window & Glass Association
