How to Clean and Re-Oil a Hardwood Deck (Annual Maintenance)
Every spring I get the same call from mates in Stirling, Aldgate and Bridgewater. “Steve, the deck looks rooted, can you come fix it?” Nine times out of ten the deck isn’t dead — it’s just thirsty. Merbau, spotted gum, blackbutt, jarrah — they all go silver-grey and feel furry inside 12 months if you don’t oil them. The fix isn’t replacement, it’s an annual oil. Not three-yearly like the Cabot’s tin label suggests if you read it sideways. Annual. The other thing every YouTube deck video gets wrong is the order of operations. Everyone fixates on which oil to buy — Cabot’s vs Sikkens vs Intergrain. It barely matters. What matters is whether you got the dirt and the grey weathered fibres off the surface before you opened the tin. A $90 tin of Cabot’s Aquadeck on a dirty deck is $90 wasted; it’ll peel in eight months. This is the routine I run on my own merbau deck on the second weekend of October, every year.
What you’ll need
- Cabot’s Deck Clean or Intergrain Reviva — 1L does about 25 m²
- A stiff-bristle deck brush on a long handle (Sabco from Bunnings, around $18)
- A garden hose with a trigger nozzle — NOT a pressure washer (more on this in Step 5)
- Cabot’s Aquadeck or Cabot’s Deck & Exterior Stain in Merbau — 4L for an average deck
- A Cabot’s deck applicator pad on a pole, plus a cheap 50 mm cut-in brush
- Drop sheets or old towels for the perimeter pavers
- Plastic gloves and shoes you don’t care about
- Painter’s tape for wall flashing and posts
- A pin-style moisture meter ($50 at Bunnings) if you want a precise readiness check
Step 1: Pick your weekend carefully
You want two consecutive dry days with no rain forecast for 48 hours after. Check the BOM site, not the iPhone weather app — the iPhone one is hopeless for SA, especially in the Hills where the microclimate flips by suburb. Temperature between 12°C and 28°C. Don’t oil in 35°C summer heat: the oil flashes off the surface before it soaks in and you get a sticky film that never dries. Late October or early March are my favourite weekends — moderate temps, predictable weather, dry timber.
Step 2: Clear and sweep the whole deck
Move every pot, the BBQ, the kids’ scooters and bikes. Sweep with a stiff broom. Get into the gaps between boards with a paint scraper or an old butter knife — leaves and gum nuts trapped between boards rot the joists below, and that’s a much bigger problem than a grey deck. While you’re down there, check fixings — a loose screw is a 30-second fix today and a sprung board in 18 months if you ignore it.
Step 3: Pre-wet the pavers and surrounding walls
Here’s the Aussie gotcha nobody warns you about. Merbau bleeds tannin. When you wet it with deck cleaner, the runoff is rust-coloured and it stains concrete pavers, sandstone, painted weatherboards and rendered walls — anything porous. Pre-wet every paver and wall around the deck with the hose first. A wet surface won’t absorb the tannin; a dry surface will, and you’ll be scrubbing rust-coloured stains off the path for the next six months. I also lay old towels along the bottom course of the rendered wall behind the deck. Cheap insurance.
Step 4: Apply deck cleaner in 2-metre sections
Wet the deck down first with the hose. Pour the Cabot’s Deck Clean into a watering can — easier than splashing it from the bottle. Apply in 2-metre sections so it doesn’t dry on you. Scrub WITH the grain using the long-handle brush. You’ll see the water turn brown immediately — that’s dead grey fibre and embedded dirt lifting. Leave it 10 minutes but don’t let it dry. Twenty years on the tools and I still see people scrubbing across the grain “to get it deeper”. You’re not getting it deeper, you’re tearing the surface fibres and leaving the deck looking corduroyed.
Step 5: Rinse with a hose, NOT a pressure washer
Every Bunnings ad shows a pressure washer on a deck. Don’t. A 2000 PSI Gerni at the wrong angle peels the soft summerwood out from between the harder latewood grain and leaves the deck looking like corduroy. Use a garden hose with a trigger nozzle on jet setting and rinse with the grain until the water runs clear. Takes longer. Looks ten times better in five years. The number of leak callbacks and replacement-board jobs I’ve done because someone took a pressure washer to a 12-year-old deck would shock you. For the right way to use a pressure washer on actual concrete, see how to pressure-wash a driveway safely.
Step 6: Let it dry — minimum 24 hours
This is where weekend warriors stuff up. Merbau looks dry after 4 hours. It isn’t. The fibres at the surface are dry; the wood underneath is still saturated, and oil applied to wet wood can’t penetrate. Wait overnight. If your deck is in deep shade or south-facing, wait 36 hours. A moisture meter showing under 18% is the precise answer; without one, look for uniformly pale boards with no dark damp patches, and a dry back-of-the-hand check across the surface.
Step 7: Mask and cut in around fixed features
Tape any aluminium flashing, the bottom of the wall behind the deck, around posts you don’t want oiled, and any glass balustrade fixings. Use a 50 mm brush to cut in along the wall, around posts, and into the gaps between boards. Work the oil right into the gap — that’s where moisture gets in and rot starts. Pay particular attention to end-grain at the board ends; it drinks oil four times faster than face-grain.
Step 8: Roll out with the applicator pad along the grain
Pour Cabot’s Aquadeck into a paint tray. Load the applicator pad. Apply along three boards at a time, working with the grain from one end to the other in a single pass. Don’t go back over wet oil — you’ll get lap marks where the oil started to set. One coat is enough on a healthy deck. If yours is genuinely thirsty (first coat soaks in within 5 minutes and looks dry again) give it a second coat after 4 hours. Twenty years on the tools and I’m still careful here; lap marks are the most visible thing you can do to a deck.
Step 9: Wipe excess after 20 minutes
Walk back over the deck with a cotton rag and wipe any pooled oil — corners, knots, the gap above a joist where oil collects. Pooled oil that dries in place stays sticky for weeks and shows every footprint. Lay the rags flat outside on concrete. Oil-soaked rags in a bin can self-combust — I’ve seen a fire in a Bridgewater shed started exactly this way. Lay them flat in the sun for 24 hours then bin them. Same applies to the applicator pad if you’re not going to use it again.
Step 10: Stay off it for 24 hours, no furniture for 48
Foot traffic on uncured oil tracks the finish off in lines. Pot plants left on uncured oil leave permanent ring marks. Cordon the deck off with a bit of string and a kids’ bedsheet. Tell the kids. Tell the dog. The dog won’t listen. Re-coat every 12 months and the deck looks like new every spring; let it go 3 years and you’re looking at a full strip-and-stain job — see how to strip and re-stain a timber deck for that one.
When to call a tradie
Annual oiling is squarely a homeowner job. Call a tradie when you’ve got rot at the joist contact points (soft, spongy boards near the wall), more than a couple of cupped or warped boards, surface checking deeper than 2 mm along the grain, or any structural movement (springiness when you walk on a section). Replacing a single board is a 30-minute hand-tool job. Replacing a whole deck is $80–$150/m² supplied and laid. If you’re seeing tannin staining bleed into a downstairs slab below the deck, you may also need a waterproofer to look at the membrane between deck and slab — AS 3740-related and not DIY.
Common screw-ups
- Skipping the pre-wet on surrounding pavers — tannin stains everything within 2 metres of the deck.
- Pressure-washing instead of scrub-and-hose — fluffed timber, faster weathering, shorter deck life.
- Oiling on damp wood — oil won’t penetrate, finish goes sticky, stays sticky for weeks.
- Mixing brands between coats — different carriers can react, blotchy absorption, expensive lesson.
- Binning oil-soaked rags directly — genuine fire risk, lay them flat outside until cured.
Cost & time
Cabot’s Deck Clean 1L: $20. Cabot’s Aquadeck 4L: $95. Applicator and brush: $15. Saturday morning plus Sunday morning of actual work — about 4 hours total across the two days, mostly waiting time during the dry. Compare against a sand-and-strip job once you’ve let the deck go three years: $400 in stripper, brushes, replacement boards and screws plus two full Saturdays. Annual oil wins on every measure.
Annual, not three-yearly. The Cabot’s tin doesn’t lie — it says “re-coat as required” — but “as required” on Aussie merbau in full sun is 12 months, every single time. Mark it in the calendar for the second weekend of October. The deck you maintain on a Saturday looks ten times better than the deck you let go for three years and try to rescue with a sander and a fresh tin. Sanding a deck is two full days you’ll never get back, plus belt-sander hire and three packs of 80-grit, and it knocks years off the boards. Cheaper, easier, faster to oil annually and never reach the sand-it-back stage. Store the unused half-tin properly too — squeeze the air out, sit a bag of sand on top of a flexible tin, or decant into glass jars filled to the brim. Air oxidises the oil and turns it gluggy. A properly stored half-tin is good for next year’s touch-ups. Do it once, do it properly.
