A grey, weathered timber deck can be brought back to life with the right preparation and products — and in most cases it's a satisfying DIY job. The key is that preparation does about 80% of the work: skip it and even the best deck coating will peel within a season. Here's how to do it properly in the New Zealand climate.
Why Timber Decks Go Grey
When untreated or uncoated timber is exposed to UV light and moisture, the lignin (the natural binder in wood) breaks down and washes away, leaving behind grey, silvery fibres on the surface. This is called weathering or greying, and it's extremely common on NZ decks given our high UV index and variable weather. The good news is that the grey layer is usually only a millimetre or two deep — the timber underneath is often still sound.
Before you start, check the deck boards for rot, soft spots, raised nails or screws, and loose fixings. Press a screwdriver into any suspicious areas; if it sinks in easily, that board needs replacing before you paint. Also check that the deck structure (joists and bearers) is in good condition.
Choose the Right Product: Paint vs Stain vs Oil
For a weathered deck you have three main options:
| Product Type | Appearance | Durability | Best For |
|---|---|---|---|
| Deck stain / semi-transparent | Shows timber grain | 2–4 years | Timber in reasonable condition |
| Solid colour deck coating | Opaque, paint-like | 3–6 years | Heavily weathered or patchy timber |
| Penetrating deck oil | Natural, low sheen | 1–2 years | Hardwoods, regular maintenance |
For a heavily greyed deck, a solid colour deck coating or a timber deck stain (semi-transparent or solid) is usually the best choice. Resene offers their popular Resene Timber & Deck range, and Dulux has the Weathershield Deck & Exterior range — both are widely available and well suited to NZ conditions. Wattyl also produces deck-specific coatings worth considering.
Always read the manufacturer's datasheet and choose a product rated for exterior horizontal surfaces — interior or wall paints are not suitable for decks.
What You'll Need
- Stiff-bristle broom and garden hose (or pressure washer on low setting)
- Deck cleaner / wood brightener (available at Bunnings or Mitre 10)
- 80-grit and 120-grit sandpaper or a pole sander
- Hammer and nail punch (or drill/screwdriver)
- Exterior wood filler for cracks
- Paintbrushes (50–75 mm), a short-nap roller, and a roller extension pole
- Appropriate primer (check your chosen topcoat's requirements)
- Your chosen deck coating
- Safety glasses, gloves, and a dust mask for sanding
Step-by-Step: Preparing the Deck
1. Clear and Clean
Remove all furniture, pot plants and anything else from the deck. Sweep thoroughly. Apply a deck cleaner or wood brightener mixed to the manufacturer's instructions — these products lift grey oxidised fibres, mould, mildew and tannin stains. Work it in with a stiff brush, leave it to dwell, then rinse well with a hose. If using a pressure washer, keep the pressure low (under 1500 psi) and always work with the grain to avoid raising the timber fibres.
2. Allow to Dry Completely
This is critical. Timber must be fully dry before coating — typically allow at least 48 hours of dry weather, longer in cooler or humid conditions. Painting over damp timber is one of the most common causes of premature peeling.
3. Sand the Surface
Once dry, sand the deck with 80-grit paper to remove any remaining grey fibres and rough grain raised by washing. Follow up with 120-grit for a smoother finish. Always sand with the grain. Vacuum or sweep away all dust.
4. Fix Any Issues
Punch any raised nails below the surface and fill with an exterior-grade wood filler. Tighten or replace any loose screws. Fill cracks and gaps as needed and allow filler to cure fully.
Applying Primer and Topcoat
Check whether your chosen deck coating requires a primer or sealer coat — many solid colour coatings do, especially over bare or heavily weathered timber. Follow the product datasheet exactly.
- Apply primer with a brush, working it into the grain. Allow to dry per the datasheet.
- Apply the first topcoat using a brush for edges and board ends, then a short-nap roller for the main field. Work in manageable sections and always maintain a wet edge to avoid lap marks.
- Apply a second topcoat once the first is dry to the touch (check the recoat window on the tin). Two coats are almost always recommended for durability.
- Board ends absorb moisture readily — pay extra attention to coating these thoroughly.
Avoid painting in direct hot sun, as the coating can dry too quickly and blister. Early morning or overcast days are ideal. Check the weather forecast — you need at least 24–48 hours of dry conditions after application.
Maintenance Going Forward
Even the best deck coating needs maintenance. Plan to clean your deck annually and inspect the coating. Most solid coatings will need a light sand and a maintenance coat every 2–4 years depending on sun exposure, foot traffic and your local climate. Coastal and high-UV locations (common across much of NZ) will need more frequent attention. BRANZ has useful guidance on exterior timber maintenance.
When to Call a Professional
Consider hiring a qualified painter if:
- The deck is large or complex in shape
- There is significant rot or structural damage (a builder may be needed first)
- You're unsure about the right product system for your timber species
- You want a guaranteed, professional finish
A professional painter will have commercial-grade equipment, product knowledge and experience with NZ conditions. You can find qualified local painters on tradedirectory.co.nz.
Safety note: Sanding old decks can generate fine timber dust — always wear a dust mask and safety glasses. If your deck was built before the 1990s and has been previously painted, there is a small chance of lead-based paint; check with WorkSafe NZ for guidance on safe handling.
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