How to Remove Old Varnish from Interior Timber Before Painting

Removing old varnish from interior timber is an essential prep step — paint applied over varnish will peel, bubble, or simply not bond properly. The good news is that with the right method and a bit of patience, most homeowners can tackle this job themselves. Here's how to do it safely and effectively.

Why Proper Preparation Matters

Varnish creates a hard, non-porous surface that paint can't grip. Even if you sand lightly and apply a coat of paint, you're likely to see adhesion failures within months — especially in high-traffic areas like skirting boards, window frames, and doors. Taking the time to fully remove or thoroughly key the old varnish is what separates a lasting paint job from one that fails early.

BRANZ research consistently shows that surface preparation is the single biggest factor in paint system longevity.

Assess What You're Working With

Before you start, check a few things:

• How thick is the varnish? Multiple coats built up over decades will need more aggressive treatment than a single thin coat.
• What's the timber? Soft timber like pine can be damaged by aggressive sanding or prolonged chemical contact. Hardwoods like rimu or matai are more forgiving.
• Is there lead paint underneath? Older NZ homes (pre-1980s (though lead paint use in New Zealand was not formally restricted until later — if in doubt, test regardless of age)) may have lead-based paint under the varnish. If you suspect this, get a lead test kit from Bunnings or Mitre 10 before sanding. If lead is present, follow WorkSafe NZ guidelines — wet sanding, respiratory protection, and careful disposal are essential.

Method 1: Sanding

Sanding is the most common approach for flat or gently profiled timber surfaces.

What you'll need

• Orbital or belt sander (for large flat areas)
• Sanding block and sheets (for detail work)
• Coarse grit (60–80) to remove the bulk of varnish
• Medium grit (120) to smooth
• Fine grit (180–240) to finish before priming
• Dust mask (P2 rated minimum), safety glasses, and hearing protection

Steps

1. Start with 60–80 grit to cut through the varnish layer.
2. Work with the grain to avoid scratching across the timber fibres.
3. Progress through grits until the surface is smooth and bare.
4. Wipe down thoroughly with a tack cloth or damp rag to remove all dust before priming.

Tip: For moulded profiles like architraves and skirting, use a sanding sponge or wrap sandpaper around a dowel to get into the curves.

Method 2: Chemical Strippers

Chemical strippers are ideal for intricate profiles, carved timber, or when you want to avoid sanding dust entirely.

• Look for solvent-based or water-based gel strippers at PlaceMakers, Bunnings, or Mitre 10.
• Water-based strippers are lower in VOCs and easier to clean up — a good choice for indoor use.
• Apply a thick coat with an old brush, cover with cling film to slow evaporation, and leave for the time specified on the product label (often 30 minutes to a few hours).
• Scrape off the softened varnish with a plastic scraper (metal scrapers can gouge soft timber).
• Neutralise the surface as directed — usually a wipe-down with water or mineral spirits.
• Allow to dry fully before sanding smooth and priming.

Safety: Work with windows open and wear nitrile gloves and eye protection. Dispose of stripped material and rags as per the product's safety data sheet.

Method 3: Heat Gun

A heat gun softens varnish so it can be scraped away. It's faster than chemicals on large flat areas but requires care.

• Keep the gun moving — holding it in one spot can scorch or even ignite the timber.
• Use a wide flat scraper immediately behind the heat gun as you work along the surface.
• Not recommended for intricate profiles where the heat can't be controlled easily.
• Always have a fire extinguisher or bucket of water nearby.

Choosing the Right Primer After Stripping

Once the timber is bare and smooth, priming is non-negotiable. A quality timber primer seals the wood, raises the grain slightly (sand lightly after it dries), and gives your topcoat something to bond to.

• Resene and Dulux both offer dedicated timber primers suitable for interior use — check their websites or ask in-store for the right product for your timber type and topcoat.
• Wattyl also has interior timber primer options worth considering.

When to Call a Professional

Consider hiring a qualified painter if:

• Lead paint is confirmed — professional painters have the equipment and training to handle this safely.
• The timber is heritage or irreplaceable (e.g., native rimu panelling) and you don't want to risk damage.
• You're dealing with large areas and don't have the tools or time.
• The varnish is heavily built up over many layers and DIY methods aren't cutting through.

A professional painter will also be able to advise on the best paint system for your specific timber and conditions. You can find qualified local painters on tradedirectory.co.nz.

Sources & Further Reading

• BRANZ – Surface Preparation Guidance
• WorkSafe NZ – Lead Paint Safety
• Resene – Interior Timber Coatings
• Dulux – Timber Primers and Paints
• Bunnings – Stripping and Sanding Products
• Mitre 10 – Painting Preparation