Priming a timber frame correctly before reglazing is one of the most important steps you can take to protect your window from rot, moisture ingress, and premature paint failure. Done well, it extends the life of both the frame and the new glazing seal significantly. This guide walks you through the process using products and practices suited to New Zealand conditions.
Why Priming Matters
New Zealand's climate — particularly in coastal, high-humidity, or high-UV regions — is tough on bare timber. When a window is reglazed, the rebate (the channel the glass sits in) is often stripped back to bare wood. Without a good primer, moisture can penetrate the timber, causing swelling, rot, and failure of the glazing compound or sealant. The NZ Building Code requires that building elements, including windows, resist moisture ingress — so getting this step right matters both practically and in terms of compliance.
Tools and Materials You'll Need
- Putty knife or chisel – for removing old glazing compound
- Coarse and fine sandpaper (80–120 grit)
- Wire brush – for stubborn old paint or compound
- Timber primer – oil-based or water-based (see below)
- Paintbrush (25–38 mm, angled sash brush works well)
- Tack cloth or damp rag – for dust removal
- Safety glasses and dust mask – especially if the old paint may contain lead (pre-1980s homes)
Step 1 – Remove Old Glazing Compound and Glass
Carefully remove the broken or old glass, then use a putty knife or chisel to scrape out all the old glazing compound from the rebate. Work methodically around the frame. Old compound can be very hard — gentle heat from a heat gun can soften it, but keep the heat moving to avoid scorching the timber.
Lead paint warning: If your home was built before 1980, the existing paint may contain lead. Check with WorkSafe NZ for safe handling guidance before sanding or scraping.
Step 2 – Sand and Clean the Rebate
Once the old compound is removed, sand the rebate and surrounding frame back to clean, sound timber. Start with 80-grit sandpaper to remove any remaining compound or flaking paint, then finish with 120-grit for a smooth surface. Use a wire brush in corners where sandpaper won't reach.
Wipe down all surfaces with a tack cloth or slightly damp rag and allow the timber to dry completely before priming. Priming damp timber is a common mistake that leads to adhesion failure.
Step 3 – Choose the Right Primer
For timber window frames, you have two main options:
| Primer Type | Best For | Notes |
|---|---|---|
| Oil-based timber primer | Bare or weathered timber, high-moisture areas | Excellent penetration, longer dry time (4–8 hrs) |
| Water-based acrylic primer | Lightly sanded or previously painted timber | Faster dry time (1–2 hrs), lower VOCs |
For bare or heavily weathered rebates — which is typical in a reglaze situation — an oil-based primer generally gives better penetration and moisture resistance. Brands like Resene, Dulux, and Wattyl all offer suitable timber primers; check the product data sheet to confirm suitability for exterior joinery and compatibility with your chosen glazing compound or sealant.
Step 4 – Apply the Primer
- Stir the primer thoroughly before use.
- Using an angled sash brush, apply a generous, even coat into the rebate, working the primer into any end grain — end grain is particularly absorbent and prone to moisture uptake.
- Pay special attention to corners and joints where water can pool.
- Allow the primer to dry fully according to the manufacturer's instructions. Don't rush this step.
- Lightly sand with 120-grit once dry, then wipe clean before applying a second coat if the timber is very porous or if the manufacturer recommends it.
Tip: Some glaziers apply a thin bed of linseed oil-based putty or a compatible flexible sealant directly onto the primed rebate before bedding the glass. This is called a back-bedding technique and helps create a weathertight seal. Check with your glazier or the sealant manufacturer for the correct product sequence.
Step 5 – Allow Full Cure Before Glazing
Don't rush into reglazing before the primer has fully cured. A surface that feels dry to the touch may not be fully cured underneath. Follow the primer manufacturer's recoat and overcoat times — these are usually listed on the tin or the product data sheet available on the brand's website.
Painting After Reglazing
Once the glass is installed and the glazing compound or sealant has cured (this can take several days to weeks depending on the product), apply your topcoat paint. The paint should overlap the glass edge by approximately 2–3 mm to form a weathertight seal between the glazing compound and the glass. This is standard practice and helps prevent water tracking behind the compound.
When to Call a Professional
While priming a timber frame is a manageable DIY task, the actual reglazing — particularly for larger panes, double glazing, or heritage joinery — is best left to a qualified glazier. Working with glass carries a real risk of cuts and breakage. If your window frames show signs of significant rot, structural damage, or if the window is part of a weathertight system (such as in a multi-storey building), consult a Licensed Building Practitioner or a professional glazier. You can find qualified local glaziers on tradedirectory.co.nz.
Also note: replacing windows in certain situations may require a building consent — always check with your local council, as Schedule 1 exemptions have specific conditions. MBIE Building Performance has useful guidance on when consent is required.
Window & Glass Association
