What’s the difference between sealing and oiling?
Sealers are film-forming finishes. They sit on top of the timber like a protective layer — think of it like lacquer on a wooden table. Most exterior deck sealers are water-based polyurethane or acrylic-urethane hybrids. They:
- Create a physical barrier against UV, rain, and dirt
- Provide a satin or semi-gloss finish
- Require less frequent reapplication (typically 2–4 years in Sydney conditions)
- Can peel or flake if they fail
- Show footprints and water spots more obviously
- Tend to darken the timber slightly and make it look “wet” or plastic-like
Oils (like tung oil, linseed oil, or penetrating deck oils) soak into the timber fibres. They:
- Nourish the wood rather than coat it
- Allow the timber to breathe and move naturally
- Maintain a more natural, matte appearance
- Highlight the wood grain beautifully
- Require much more frequent reapplication — typically every 6–12 months in Sydney’s harsh conditions
- Won’t peel because they’re absorbed, but will gradually fade to grey
- Show every footprint and water splash between coats
- Cost significantly more in labour over the life of the deck
Timber type matters — a lot
Not all timbers work equally well with both methods.
Best for sealing:
- Hardwoods like jarrah, karri, and ironbark — these dense, oily timbers don’t absorb oil easily, so a sealer bonds better and lasts longer
- Pressure-treated pine — the treatment makes these timbers less receptive to oils; a sealer works much better
- Composite decking — always sealed or coated, never oiled
Best for oiling:
- Merbau — this timber is naturally oily and loves penetrating finishes. Oiling brings out its warm chocolate tones beautifully
- Cumaru — similar to merbau in colour and density; oiling looks stunning
- Kwila — an Indonesian hardwood that ages gracefully with regular oiling
- New timber decks in general — if you want maximum beauty in year one, oil gives you that warm, glowing look that a sealer can’t match
Cost comparison: sealing vs oiling over 10 years
This is where the maths get real for Sydney homeowners. Sealing approach (80 m² deck): initial seal ~$2,000–$3,500, resealing every 3–4 years ~$1,500–$2,500 per application, 10-year total ~$7,000–$10,000. Oiling approach: initial oil ~$1,500–$2,500, recoating every 6–12 months ~$1,200–$2,000 per application, 10-year total ~$13,000–$20,000+. Sealing wins on cost and convenience. Oiling wins on aesthetics — if you can afford the maintenance commitment.
Sydney’s climate: the real-world reality
Sydney sits in a perfect storm for timber deck deterioration. Intense UV from November to February, salt spray in coastal areas, humidity swings, and frosts inland all stress timber continuously. In these conditions, sealed timber performs better. If you live in coastal Sydney (Manly, Cronulla, Dee Why, Bondi), sealing is almost essential because of salt spray corrosion. If you’re inland, you have slightly more flexibility.
Real talk: what we recommend
At 5 Star Decking, here’s what we actually advise: For jarrah, karri, ironbark, or pressure-treated pine: seal it. Maintenance is simple, lifespan is 3–4 years, and you won’t regret it. For merbau or cumaru, if you’re a purist: oil it — but only if you’re prepared to recoat every 6–9 months. For merbau or cumaru, if you’re realistic: seal it initially, reassess in 2–3 years. For composite decking: seal or coat only; never oil. For coastal properties: seal. Oil doesn’t hold up to salt spray long enough to justify the cost. The worst choice is doing nothing. Unsealed timber in Sydney’s sun will fade to grey within 18 months and start checking and splintering within 2–3 years.
Ready to protect your deck properly?
Whether you’re deciding between sealing and oiling before you book your new deck, or your existing deck needs a refresh, we can advise on the best finish for your specific timber, location, and maintenance tolerance. 5 Star Decking has installed and finished hundreds of Sydney decks. We’ll walk you through the lifespan, cost, and maintenance reality of each option — no upsell, just honest advice.
Contact us for a deck assessment or finish consultation: Get a free consultation
NSW Builder’s Licence: 395250C
Service areas: All of Sydney and surrounding regions
Phone: 0433 334 415
Posted by 5 Star Decking — Sydney’s trusted deck builders
