Replacing a broken or damaged pane of glass is one of the most common glazing tasks. For small single-glazed windows in accessible locations, it's within reach of a careful DIYer. For anything else — double-glazed units, large panels, glass above ground floor, or any safety glass location — use a professional glazier. This guide covers both timber frame putty glazing and modern aluminium frame systems.

When to Call a Professional

Before starting, honestly assess whether this is a DIY job: • Double-glazed units (IGUs) must be ordered to size and have a minimum rebate depth — not suitable for DIY • Any panel over roughly 0.6m × 0.8m is difficult to handle safely without assistance and proper suction equipment • Windows above ground floor present fall risks • Any location requiring safety glass under AS 1288 — shower screens, doors, glass near floor level — must have certified toughened or laminated glass installed correctly. See Understanding AS 1288 for which locations require safety glass

If in doubt, get a professional glazier to quote. The cost of getting reglazing wrong — a panel that falls out, incorrect glass type, or a compliance failure — far exceeds the cost of professional installation.

What You Need

Gather everything before starting: • Replacement glass (measure and order before beginning — see below) • For timber frames: glazing putty, glazing points, linseed oil or timber primer • For aluminium frames: replacement rubber glazing bead or gasket (if needed), neutral-cure silicone • Setting blocks (EPDM, 100mm long, appropriate width) • Plastic glazing packers in 2–3mm thickness • Putty knife and glazing knife • Glazing shovel or thin flat screwdriver for packer insertion • Glass cleaner and clean cloths • Cut-resistant gloves rated Level 5 — mandatory throughout • Safety glasses • Drop sheet or heavy cardboard to catch fragments

Step 1 — Remove the Broken Glass Safely

Put on your gloves and safety glasses before touching anything. If the glass is cracked but still in the frame, score it into manageable pieces (roughly 200mm × 200mm) using a wheel cutter, then press each piece inward while supporting from the other side. Never pull glass toward you — push it away from your face.

Place every fragment immediately into a rigid, puncture-resistant container. Never put broken glass in a plastic bag — the weight will cause a bag failure and broken glass on the floor creates hazards for everyone on site.

Step 2 — Remove Old Glazing Materials

For timber frames with putty glazing: • Work around the rebate with a glazing knife or chisel, levering out old putty. Tap the chisel with a mallet for hardened putty — don't force it and risk damaging the timber • Remove all glazing points (small metal clips) with pliers or a screwdriver • Sand the rebate lightly with coarse sandpaper to remove residue • Apply linseed oil or a dedicated timber primer to all bare wood in the rebate. This step is critical — unprimed timber absorbs oil from the new putty, causing it to dry out and crack within a year or two

For aluminium frames with rubber gaskets or snap-in beads: • Insert a stiff putty knife or flat screwdriver at a corner of the glazing bead and lever it out. Work around the perimeter • Remove the glass and inspect the gasket condition — replace if it's cracked, compressed, or has lost its cross-sectional shape • Clean the rebate channel with a cloth and IPA (isopropyl alcohol)

Step 3 — Measure and Order Your Glass

Measure the rebate opening — width and height — and deduct 3mm from each dimension to allow 1.5mm clearance per side. See How to Measure for Replacement Glass for full detail on measuring technique and clearance allowances.

Use the Glazing Calculator to confirm the panel weight — this tells you whether you can safely handle the panel alone or need assistance, and whether any mechanical lifting aids are needed.

Order from a glass supplier rather than a hardware store. Most glass suppliers will cut and supply glass to the public without requiring you to use their installation service. Specify the glass type clearly — for any safety glass location, specify toughened or laminated glass.

Step 4 — Prepare the Frame for the New Glass

For timber frames: Apply a thin, continuous bed of fresh putty around the rebate before the glass goes in. Press the putty into the rebate and smooth it flat with a putty knife — this is the bedding putty, which creates a continuous weatherproof seal under the glass. Don't skip this step; glass set directly on bare timber without a putty bed will flex under wind pressure and may crack.

For aluminium frames: Place EPDM setting blocks in the rebate at the quarter points — approximately 25% in from each corner along the bottom edge. These support the weight of the glass on the frame and prevent stress fractures from the glass bearing directly on aluminium.

Step 5 — Set the Glass in the Frame

Lower the glass into the rebate with a helper if needed. Position it centrally side to side using plastic packers inserted with a glazing shovel — maintain consistent clearance on both sides. The bottom of the glass should rest on the setting blocks, not directly on the frame. Check that the glass is not under any torsional stress — it should sit naturally without you needing to hold it.

Step 6 — Secure the Glass

For timber frames: Push glazing points into the timber every 150–200mm around the full perimeter using a glazing knife or screwdriver. Apply face putty around the perimeter by pressing it firmly into the joint between the glass and the frame. Draw a putty knife at a consistent 45° angle around the perimeter to form a clean chamfer, finishing at the sight line. Wet the blade slightly with linseed oil for a smoother finish.

Allow 2–3 weeks before painting over putty — painting too early traps moisture and causes premature failure. Check after one week and press down any surface cracks that appear as the putty cures.

For aluminium frames with snap-in beads: Snap the glazing bead back into position starting at the centre of each run and working outward to the corners. The bead should seat fully with no gaps or proud sections. Apply a thin bead of neutral-cure silicone at the glass-to-bead junction on the weather side if the original installation included this.

For silicone-only frames: Apply a continuous bead of neutral-cure silicone around the perimeter, tool to a smooth, consistent finish with a spatula, and remove excess immediately with a cloth dampened with mineral spirits. Allow to cure fully before the frame is exposed to rain — typically 24 hours.

Step 7 — Clean and Inspect

Clean the glass surface with glass cleaner. Inspect from both sides for consistent sealant application, correct packer placement, and clean sight lines. For timber putty work, inspect the chamfer for any voids or gaps — these should be filled before the putty skins over.

Common Mistakes

Measuring the existing glass rather than the rebate opening — leads to incorrect panel size
Not deducting clearance — glass too large to fit correctly in the frame
Using standard glass where safety glass is required
Not priming timber before applying putty — leads to rapid putty failure
Skipping setting blocks — glass bearing directly on the frame can stress crack over time
Using acetic-cure silicone (vinegar-smell) on aluminium or stone surrounds — causes staining; use neutral-cure

Frequently Asked Questions

How do I know if my window needs safety glass?

Safety glass is required by AS 1288 in locations where a person could fall into or through the glass: shower screens, any glass with its bottom edge less than 1000mm from the floor, glass within 300mm of a door, balustrades, overhead glazing, and swimming pool fencing. If uncertain, always use safety glass — it's never wrong to use it where it isn't required.

Can I repair a crack instead of replacing the glass?

For single-glazed windows, cracks generally need full replacement — thermal movement causes cracks to propagate. Windscreen-style chip repair resins exist for small impacts in laminated glass but are cosmetic rather than structural. For double-glazed units, a cracked pane means the entire unit needs replacing; the seal is compromised.

What putty should I use for timber windows?

Traditional linseed oil putty is the standard for timber frames. It remains slightly flexible after curing and accepts paint well. Water-based putty is available and easier to clean up but has inferior long-term durability in exposed locations. Never substitute silicone for putty in traditional timber frames — it doesn't adhere well to painted timber and looks wrong.

How long does reglazing take?

A single small window under 0.5m² takes a professional glazier 1–2 hours including glass fitting and sealing. A DIY first-timer should allow 3–4 hours for the same job. Larger panels, multi-pane windows, or access difficulties add proportionally.

Can I buy glass cut to size from a hardware store?

Some large hardware stores offer a cutting service for standard annealed glass. The range is limited — no toughened, laminated, or IGUs. For any safety glass location or non-standard requirements, use a glass supplier or glazier. Many glass suppliers will supply cut-to-size glass to the public on the same day or next day.

How to Reglaze a Window: A Step-by-Step Guide