What Type of Glazing Putty Should I Use for Timber Windows?

For timber windows, you have two main options: traditional linseed oil putty or a modern acrylic glazing compound. Both can do the job well, but the right choice depends on your window type, the local climate, and how much maintenance you're prepared to do. Here's what you need to know before heading to the hardware store.

Traditional Linseed Oil Putty

Linseed oil putty has been used on timber-framed windows for well over a century, and it remains a solid choice — particularly for older villas and bungalows where you want to keep things authentic. It's made from whiting (ground chalk) and raw linseed oil, giving it a smooth, workable consistency.

Pros

• Excellent adhesion to bare timber and glass
• Paintable once a skin has formed (usually 7–14 days, depending on conditions)
• Widely available at Bunnings and Mitre 10
• Cost-effective for large jobs

Cons

• Slow to cure — can take weeks to fully harden
• Becomes brittle and cracks over time if not painted and maintained regularly
• Needs a primed or sealed timber rebate before application, otherwise the timber absorbs the oil and the putty fails prematurely
• Not ideal in very wet or exposed coastal locations without diligent upkeep

Important prep tip: Always prime bare timber rebates with a wood primer or a thin coat of linseed oil before applying linseed putty. This prevents the timber from drawing the oil out of the putty, which causes it to dry out and crack far too quickly.

Modern Acrylic Glazing Compounds

Acrylic-based glazing compounds (sometimes labelled as glazing sealants or flexible glazing putty) are increasingly popular for NZ homeowners. They remain flexible after curing, which helps them cope with the timber movement that comes with our seasonal temperature swings — from humid Northland summers to frosty Otago winters.

Pros

• Flexible when cured, so less prone to cracking as timber expands and contracts
• Faster drying — often paintable within 24–48 hours
• Good adhesion to primed timber and glass
• Better suited to exposed or coastal environments
• Easier to tool and clean up (water cleanup before curing)

Cons

• Generally more expensive than linseed putty
• Some products don't accept paint as readily — always check the manufacturer's data sheet
• Not always appropriate for heritage restoration work where authenticity matters

Brands like Sika offer flexible sealant products suitable for glazing applications. Always read the product data sheet to confirm suitability for your specific situation.

Which Should You Choose?

Here's a quick comparison to help you decide:

Application Tips for Best Results

1. Remove all old, loose putty using a hacking knife or chisel. Take care not to crack the glass.
2. Clean the rebate thoroughly — remove dust, old paint flakes, and any rot. Treat any rot before proceeding.
3. Prime bare timber with a suitable wood primer and allow to dry fully.
4. Bed the glass in a thin layer of putty (the bedding layer) before pressing the pane into place.
5. Apply the face putty at roughly a 45-degree angle, tooling it neatly with a putty knife or glazing tool.
6. Allow to cure as per the product instructions before painting. Painting too early traps moisture and causes adhesion failure.
7. Paint over the putty so the paint just overlaps onto the glass by 1–2 mm — this seals the putty-to-glass joint and is critical for longevity.

For guidance on maintaining your home's weathertightness — which glazing plays a part in — BRANZ is an excellent NZ resource.

NZ Building Code Considerations

Replacing glass in an existing timber window is generally exempt from building consent under Schedule 1 of the Building Act, provided you're doing like-for-like replacement and not altering the window opening. However, if you're replacing single glazing with double glazing, or making structural changes, you should check with your local council first. The MBIE Building Performance website has useful guidance on consent requirements.

If your home is a rental, note that the Healthy Homes Standards set minimum requirements around glazing and draught stopping — see Tenancy Services for details.

When to Call a Professional

While reglazing a small pane is a manageable DIY task for a confident homeowner, there are times when it's best to bring in a qualified glazier:

• Large panes or heavy glass — handling risk is significant
• Safety glass requirements — NZS 4223 sets out where safety (toughened or laminated) glass must be used, such as near doors, low-level panels, and bathrooms. Getting this wrong can be a serious safety hazard
• Rotted or damaged frames — structural repairs may require a Licensed Building Practitioner
• Heritage or character homes — specialist knowledge helps preserve authenticity and value
• You're unsure about the glass type needed — a professional glazier will specify the correct glass to meet the NZ Building Code

You can find qualified local glaziers on tradedirectory.co.nz to get the job done safely and correctly.

Sources & Further Reading

• BRANZ – Building Research Association of NZ
• MBIE Building Performance – Consent information
• Tenancy Services – Healthy Homes Standards
• Sika NZ – Sealants and glazing products
• Bunnings NZ – Glazing putty and supplies
• Mitre 10 NZ – Glazing supplies