How to Clean and Re-Oil a Hardwood Deck (Annual Maintenance)

By Steve — flooring and wet-area specialist, Adelaide Hills SA.

Every spring I get the same call from mates in Stirling and Aldgate: “Steve, the deck looks rooted, can you come fix it?” Nine times out of ten the deck is fine — it’s just thirsty. Merbau, spotted gum, blackbutt — 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 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 actually 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 annual routine I run on my own merbau deck on the second weekend of October, every year, and it takes a Saturday morning plus a Sunday morning. Don’t try to do it in one day — the wash needs to dry overnight.

What you’ll need

• Cabot’s Deck Clean (or Intergrain Reviva) — 1L does about 25 m²
• Stiff-bristle deck brush on a long handle (Sabco from Bunnings, $18)
• Garden hose with a trigger nozzle (NOT a pressure washer — more on this)
• Cabot’s Aquadeck or Cabot’s Deck & Exterior Stain in Merbau — 4L for an average deck
• Cabot’s deck applicator pad on a pole, plus a cheap 50 mm brush for edges
• Drop sheets or old towels for the perimeter pavers
• Plastic gloves and old shoes you don’t care about
• Painter’s tape for the wall flashing/posts

Step 1: Pick your weekend

You want two consecutive dry days with no rain forecast for 48 hours after. Check BOM, not the iPhone weather app — the iPhone one is hopeless for SA. 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.

Step 2: Clear and sweep

Move every pot, the BBQ, the kids’ scooters. 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 bigger problem than a grey deck.

Step 3: Pre-wet the pavers and 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 — 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

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 the dead grey wood fibre and dirt lifting. Leave it 10 minutes but don’t let it dry.

Step 5: Rinse — with a hose, not a pressure washer

I know every Bunnings ad shows a pressure washer on a deck. Don’t. A 2000 psi gerni at the wrong angle peels the soft early-wood out from between the harder late-wood 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 better in five years.

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, wait 36 hours.

Step 7: Mask and cut in

Tape any aluminium flashing, the bottom of the wall behind the deck, and around any posts you don’t want oiled. Use a 50 mm brush to cut in along the wall, around posts, and into the gaps between boards. Work the oil into the gap — that’s where moisture gets in and rot starts.

Step 8: Roll out with the applicator pad

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 of the board to the other in a single pass. Don’t go back over it — if you do, you’ll get lap marks where the oil started to set. One coat is enough on a healthy deck. If yours is genuinely thirsty (the first coat soaks in within 5 minutes and looks dry again) give it a second coat after 4 hours.

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 it. Lay them flat in the sun for 24 hours then bin them.

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. Tell the kids. Tell the dog. The dog won’t listen.

A note on oil brands — they’re more similar than you think

Cabot’s Aquadeck is water-based and easier to work with — low odour, soap clean-up, recoats in 4 hours. Cabot’s traditional Deck & Exterior Stain is solvent-based, smellier, but penetrates harder timbers like spotted gum more deeply on the first coat. Sikkens Cetol Deck is the trade favourite — slightly more durable but twice the price. Intergrain UltraDeck is the supermarket-tier option and honestly does the job on standard merbau. The brand argument matters less than the prep argument. A clean deck takes any decent oil. A dirty deck rejects all of them.

Don’t mix brands between coats — the carriers can react and you’ll get patchy absorption. Stick with one brand for the life of that deck. If you’re starting from raw timber on a new deck, Cabot’s Natural Decking Oil for the first coat is hard to beat because it gets the timber sealed before you commit to a colour-tinted product.

The Steve rule

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 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 then try to rescue with a sander and a fresh tin. Sanding a deck is two full days you’ll never get back, plus the cost of belt-sander hire and three packs of 80-grit. Cheaper, easier, faster to oil annually and never reach the sand-it-back stage.

One last thing: store the unused oil correctly. Cabot’s Aquadeck goes off in 6-12 months once opened. Squeeze the air out of the tin if it’s a flexible plastic one (sit a bag of sand on top), or decant remaining oil into smaller glass jars filled to the brim. Air is what oxidises the oil and turns it gluggy in the tin. A properly stored half-tin is good for next year’s touch-ups.

Got a deck horror story or a brand of oil you swear by? Send us a write-up.