Window putty is the firm, paintable seal that holds a single pane of glass in a timber sash and keeps out rain and draughts. When it cracks, shrinks, or falls away, you can usually fix the window by removing the failed putty and repainting it, as long as the glass and timber are sound. If the glass is broken, the sash is rotting, or the paint may contain lead, calling a glazier is often the safer choice.
This guide is for Sydney owners of older homes with timber, single-pane windows. It explains how to spot failing putty, how to decide between repair and replacement, how to re-putty a pane step by step, and when a professional is better suited to handle the job.
What Is Window Putty and What Does It Do?
Window putty, also called glazing putty, is a dough-like sealant pressed into the rebate of a timber sash to hold the glass in place and shed water. Traditional putty is linseed oil mixed with whiting (finely ground chalk). Once it skins over and is painted, it forms a weatherproof bevel that can last for decades.
A typical traditional mix is about 15% linseed oil to 85% calcium carbonate, according to the Museum of Fine Arts Boston’s CAMEO materials database. The same source notes that some older putties also contained lead pigments to speed up drying, which matters when you remove them.
Putty does two jobs on most older windows:
- Back bedding: a thin layer between the glass and the timber rebate that cushions the pane and stops water from creeping behind it.
- Face putty: the angled bevel on the outside that seals the glass edge and sheds rain.
Small metal glazing points (also called sprigs) hold the glass in place mechanically. The putty seals it. Aluminium and uPVC windows generally use rubber gaskets or sealants instead, so putty problems are mostly a timber-window issue.
Signs Your Window Putty Needs Attention
Check the outside face of each pane. Cracks, gaps between the putty and glass, missing sections, or putty that has turned chalky and crumbly all mean the seal is failing. Rattling glass, draughts and water stains on the inside sill are common symptoms that follow.
Look for:
- Hairline or deep cracks running along the bevel
- Gaps where the putty has pulled away from the glass or timber
- Missing chunks, often on the bottom rail where water sits longest
- Bare putty with little or no paint left on it
- Glass that rattles when the sash moves or the wind picks up
- Water stains, flaking paint or soft timber on the sill or bottom rail
Rattling can also come from worn sash hardware or loose beads, so check the whole window. Small cracks in otherwise firm putty can often be patched. Widespread cracking or crumbling usually means the whole pane needs new putty.
Should You Repair or Replace Window Putty?
Repair the putty when the glass is intact, the timber is sound, and the problem is limited to the seal. Replace the glass, sash or window when the glass is cracked, the timber is rotten, or you need better comfort than single glazing can give. Suspected lead paint or a pane that may need safety glass are reasons to call a glazier.
| Situation | Best option | DIY suitable? |
| A few small cracks; the surrounding putty is still firm | Patch the damaged section, then paint | Usually |
| Putty is crumbling or missing along one or more sides | Remove and replace all putty on that pane | Yes, with care |
| Cracked or broken glass | Replace the pane, then replace it | Small panes possibly; a glazier if safety glass may be required |
| Soft or rotten timber in the rebate or sash | Repair the timber first, or replace the sash | Usually, a professional job |
| Home built before 197,0 and pains are untested | Test for lead before disturbing anything | Not until tested |
| Many windows, upper storeys or heritage frames | Professional reglazing | Generally no |
| Rooms too hot or cold, even with the sound putty | Consider secondary glazing, low-e glass or double glazing | Get advice |
New putty does not bond to loose, crumbling putty, so patching only works where the putty around the repair is still well attached. If you can lift sections away with a fingernail, plan for a full repute.
Check for Lead Paint Before You Start
If your home was built before 1970, treat the window paint as possibly containing lead until a test shows otherwise. Scraping, sanding or heating lead paint releases dust and fumes that are hazardous, particularly for children and pregnant women. Old putty can contain lead as well.
The City of Sydney notes that paints from the 1950s could contain up to 50% lead, and that lead content was not limited to 1% until 1970. The Australian Government’s Lead Alert guide to lead in house paint warns that lead paint is dangerous when its dust, flakes or fumes are swallowed or inhaled.
Before you start:
- Use a lead test kit or arrange a laboratory test of a paint chip.
- If lead is present, avoid dry sanding and high heat, which create the most dust and fumes.
- Keep children, pregnant people and pets away from the work area.
- Lay drop sheets to catch debris and clean up with a damp cloth, not a broom.
- If you are unsure, ask a professional to do the work using lead-safe methods.
How to Replace Window Putty on a Single-Pane Window
To replace window putty, remove the old putty and loose paint, clean and prime the rebate, re-secure the glass with glazier’s points, press in new putty and tool it to a smooth bevel, then paint once it has skinned over. Allow roughly 15 minutes to an hour per pane, depending on its size and how stubborn the old putty is.
Tools and materials
Tools: stiff putty knife, utility knife, scraper or razor-blade scraper, pliers, vacuum cleaner, sandpaper, paintbrush, and a heat gun with a heat shield or a sheet of metal (only once lead has been ruled out). A caulking gun is needed only for tube glazing compound.
Materials: linseed oil putty or an acrylic glazing compound rated for timber windows, glazier’s points, primer suited to the putty you choose, exterior paint, and replacement glass if needed.
Safety gear: safety glasses, cut-resistant gloves and a suitable dust mask or respirator.
Step-by-step method
- Work on a bench if you can. Removing the sash and laying it flat on a clean, sturdy surface makes the job easier and the finish neater. Panes can be repositioned in place if the sash cannot come out.
- Remove loose putty. Slide a utility knife or putty knife into the cracks and lever the old putty out. Work along the rebate without gouging the timber.
- Soften stubborn putty carefully. Only after ruling out lead, use a heat gun on a low setting, keep it moving and shield the glass with metal. Heat held on one spot can crack the pane.
- Deal with points and broken glass. Pull out damaged glazier’s points with pliers. If a pane is broken, cover it with a cloth, wear gloves and eye protection, and carefully remove the pieces.
- Clean the rebate. Scrape back to clean timber, remove loose or peeling paint, and vacuum up dust and crumbs.
- Prime the bare timber. Dry timber draws oil out of fresh putty, which can cause it to crack early. Apply primer to the rebate and let it dry as directed.
- Bed and secure the glass. If the glass was removed, run a thin layer of bedding putty, press the pane in evenly, then push in glazier’s points about every 200 mm, with at least two per side.
- Apply the face putty. Knead the putty until soft and warm, then press it firmly into the rebate with your thumb so there are no gaps or air pockets.
- Tool the bevel. Draw the putty knife along each side at about 45° in a smooth, continuous stroke. Keep the top edge of the bevel just below the line of the inside timber so the putty is not visible from indoors.
- Clean up. Trim any bedding putty that has squeezed out inside, and wipe the glass clean.
Curing and painting
Linseed oil putty must form a skin before you paint it, which can take from several days to a few weeks, depending on the product and the weather. Acrylic compounds can usually be painted sooner. Always follow the time on the product label.
Prime, then paint the putty, carrying the paint a millimetre or two onto the glass. This seals the joint between putty and glass against water. Unpainted linseed putty dries out and cracks faster, so painting is part of the repair, not just a finishing touch.
Linseed Oil Putty vs Acrylic Glazing Compound
Linseed oil putty is the traditional choice for timber windows and is well-suited to heritage work. It is applied by hand and takes longer to cure before painting. Acrylic or latex glazing compounds often come in tubes, are easier for beginners and can usually be painted sooner. Check the label confirms the product suits face glazing on timber.
| Feature | Linseed oil putty | Acrylic or latex glazing compound |
| Typical form | Tub, knife grade | Tube for a caulking gun, or tub |
| Application | Kneaded and tooled by hand | Applied as a bead, then tooled |
| Time before painting | Longer; check the label | Shorter; check the label |
| Finish | Crisp, traditional bevel | It can be harder to tool neatly |
| Best suited to | Heritage and traditional timber sashes | Small repairs and first-time DIYers |
| Paint needed afterwards | Yes | Usually recommended |
If you are matching existing putty on a period home, linseed oil putty gives the most consistent look.
When to Call a Glazier
Call a glazier when glass is cracked or needs replacing, when a pane may need safety glass, when paint may contain lead, when windows are hard to reach, or when several windows need reglazing. A glazier can also tell you whether a repair is still worthwhile or the sash is past saving.
It is usually time to get professional help if:
- The glass is cracked, broken or loose in the frame
- The pane is in or beside a door, near the floor or in a bathroom
- Lead paint is confirmed or suspected
- The window is on an upper storey or needs a ladder to reach
- The timber rebate or sash is soft, split or rotting
- You have more windows than you have weekends
In NSW, residential building work worth more than $5,000 (including GST, labour, and materials) must be carried out by a licensed contractor, including glazing. You can confirm a business’s licence with the NSW Fair Trading home building licence check. Membership of the Australian Glass and Window Association is another sign that a glazier keeps up with industry standards.
Majestic Glass provides glazing services across Sydney, including reglazing existing windows so that damaged or ageing glass can be replaced while keeping the original frame where it is, provided it is in suitable condition.
Replacing broken glass and safety glass rules
When a pane is replaced, the new glass must suit its location. AS 1288: Glass in buildings sets out the requirements for glass that people may come into contact with. Some locations need Grade A safety glass, which is toughened or laminated, rather than ordinary float glass.
That means swapping like for like is not always appropriate on an older window, particularly around doors and in low-level panes. A glazier can confirm what is needed and supply safety glass cut to size. For urgent breakages, see our tips for emergency window glazing.
When it is time to upgrade the window
New putty stops leaks and draughts around the glass, but it does not change how much heat passes through it. The Australian Government’s Your Home guide to glazing notes that single glazing with clear glass is not very efficient, and that low-e glass or double glazing performs better.
Draughts still matter: Sustainability Victoria estimates up to 25% of winter heat loss from existing houses comes from air leakage. Sealing putty is a worthwhile first step before you consider bigger changes.
If you want more comfort without losing the look of period windows, options include secondary glazing, energy-efficient glass or new custom windows. Our guide to glazing options for sash windows compares them. If your home is heritage-listed or in a heritage conservation area, check with your council before changing windows.
Get Your Windows Weathertight Again
Sound window putty keeps older timber windows dry, quiet and draught-free. Small cracks are a manageable DIY job once you have ruled out lead. Broken glass, rotten timber, safety-glass locations and multi-window jobs are where a glazier saves time and risk.
Not sure whether your windows need new putty, new glass or a new sash? Call Majestic Glass on 1800 452 946 or request a free quote, and our Sydney glaziers will advise on the right fix for your home.
Frequently Asked Questions
How long does window putty take to dry?
Linseed oil putty forms a paintable skin within several days to a few weeks, depending on the product, temperature, and humidity, and continues curing beneath the surface for much longer. Acrylic compounds are usually ready to paint sooner. Follow the time on the label rather than a general rule.
Can I put new window putty over old putty?
Only where the old putty is firm and well attached will new putty bond; it will not bond to loose, cracked, or crumbling material, so remove anything that lifts easily. Patching over failed putty traps water and usually fails again within a season or two.
Is old window putty dangerous?
It can be. Older putty sometimes contains lead, and the paint over it in homes built before 1970 often does as well. Test before disturbing it, avoid dry sanding and heat guns on lead paint, and consider a professional if lead is confirmed.
Can I use silicone instead of window putty on timber windows?
Standard silicone is generally not paintable and is not designed for face glazing timber sashes, so it can leave an exposed seal that weathers poorly. Use a putty or glazing compound labelled for timber windows, or ask a glazier which product suits your frames.
How much does it cost to have a window repaired in Sydney?
There is no single price. Cost depends on the number and size of panes, access, whether glass needs replacing, whether lead-safe methods are needed, and the condition of the timber. An on-site inspection gives the most accurate quote.