Cleaning a wooden deck without a pressure washer

Øens HåndværkerCentralPublished August 18, 2026 · 9 min. read

You clean a wooden deck without a high-pressure washer using lukewarm water, a stiff scrubbing brush, and an approved algae remover. Brush along the grain of the wood, let the product work according to the label, and rinse with a garden hose at low pressure. This method removes algae and dirt without raising the wood fibres. A very overgrown deck typically requires two passes.

• 175 kr/m2Including VAT and a standard finish, from 36 m2
• 24 hoursReply with a fixed price
• Workmanship guaranteeOn all work performed

The most important in 30 seconds

Gentle cleaning with a brush, water, and an approved agent removes algae without wearing down the wood. Five points determine the result:

• High pressure cuts away the soft springwood between the growth rings and raises the fibres. The wood then absorbs more water and becomes overgrown again faster.
• The gear is inexpensive: a stiff scrubbing brush on a handle, a garden hose, a bucket of lukewarm water, and wood soap.
• Algae removers are biocides. The Danish Environmental Protection Agency states that the person marketing the biocide product in Denmark is responsible for ensuring that the product is approved, and you can see the approval on the label.
• Tiles, concrete, and driveways can be safely high-pressure cleaned professionally. On wooden decks, we keep the high-pressure away.
• If the boards are grey, rough, and splintered, cleaning won't help - the deck needs to be sanded and oiled.

Why shouldn't you high-pressure wash your wooden deck?

Because the water jet removes wood, not just algae. The high pressure cuts away the soft springwood between the hard growth rings, raises the fibres, and leaves a rough surface. Rough wood retains water and dirt, so the deck becomes overgrown faster next season, and the oil has a shorter lifespan.

The starting point is difficult in itself. In Træinformation's handbook TRÆ 74 Wooden Decks and Rooftop Terraces (2nd edition, March 2025, 135 pages), the formulation reads: "Using wood horizontally and freely exposed to water and weather is probably the most challenging use of wood imaginable." When the starting point is so exposed, gentle cleaning is not a detail, but what determines how many seasons the boards will last. Tile and concrete coverings are a completely different matter: there, professional high-pressure cleaning is effective, and the choice is between high-pressure cleaning or algae remover.

What can you clean your wooden deck with?

With a stiff scrubbing brush, lukewarm water, and either wood soap or an algae remover approved for algae control. The soap handles dust, pollen, and greasy dirt. The algae remover tackles the green and black growth that sits in the wood's pores and cannot be brushed off with water alone.

• Stiff scrubbing brush on a long handle with synthetic bristles
• Garden hose with a gentle shower attachment, not a high-pressure jet
• Bucket of lukewarm water and wood soap or soft soap
• Algae remover with documented approval on the label
• Joint scraper or plastic spatula for leaves and soil between the boards
• Protective gloves and safety goggles suitable for the product

There is no single specific product called deck cleaner. It is a collective term for soaps, wood cleaners, and algae removers, and therefore the label is your only point of reference. Products marketed for algae control are biocides and are covered by the Biocidal Products Regulation (EU) No 528/2012. The Danish Environmental Protection Agency's review of the biocide rules states that the person marketing the biocide product in Denmark is responsible for ensuring that the product is approved. In addition, all classified biocide-containing products sold after June 1, 2015, must bear CLP labeling. A product that merely calls itself a deck cleaner is therefore not considered an algae remover.

How to clean your wooden deck step by step

The order matters more than the effort, and a typical residential deck usually takes a morning, in our experience. Work in the shade on a dry day with no rain expected for the next few hours, so the product isn't washed away before it has had a chance to work.

1. Clear the deck completely and sweep loose dirt, leaves, and grit off the boards.
2. Clean the joints between the boards with a joint knife. Wet soil in the joints retains moisture and restarts algae growth.
3. Water the entire surface thoroughly with a garden hose at low pressure so the wood doesn't absorb the product unevenly.
4. Apply soapy water or algae remover to a few square metres at a time. The dosage and reaction time on the label are part of the product's approval, not a suggestion.
5. Scrub along the grain of the wood, never across the fibres. Take extra time near railings, steps, and edges facing north.
6. Rinse thoroughly and let the deck dry completely. If it needs to be oiled afterward, the wood must be dry all the way through, typically a couple of dry days after cleaning.
7. Finally, inspect for loose screws, splinters, and cracked boards while the surface is clean and visible.

If the work needs to be put into a regular rhythm throughout the year, the annual plan can be found in our guide to preparing the wooden deck for the season.

Which method suits the condition of your deck?

The appearance of the deck determines the method. A green film requires soap and a brush, while grey and fibrous wood requires sanding, no matter how long you scrub. The table below shows the assessment we make when we are at a deck and need to decide whether it should be cleaned or sanded.

Do home remedies like vinegar, bleach, and soda work?

Only partially. Acetic acid and bleach whiten the green colour, but do not remove algae's grip in the wood's pores, and both can discolor wood, attack screws and fittings, and scorch plants along the deck. Soda is strongly alkaline and can make the surface dark and fuzzy.

The difference lies in the approval. A product marketed for algae control must be approved for that specific purpose, and approved products can be looked up in the Danish Environmental Protection Agency's database of pesticides. Household bleach is sold as a cleaning agent and is not an approved algae remover for decks. If you want to try it yourself, the mildest and most predictable way is still water, a brush, and a mild cleaning agent. If the entire area needs to be done in one go, that is the task behind our professional outdoor cleaning and algae treatment.

How often should you clean your wooden deck?

Twice a year is suitable for most Danish decks: a thorough cleaning in early spring before the furniture comes out, and a light cleaning in autumn when leaves and seeds have settled on the boards. Decks in shade or under trees need more frequent cleaning.

The climate is the explanation. DMI's climate normals for Denmark show 746.2 mm of precipitation and an average annual temperature of 8.3 degrees Celsius for the normal period 1981-2010, while DMI's preliminary figures for 1991-2020 are 759.1 mm. Mild, humid, and without long frost periods are precisely the conditions in which algae and green growths thrive, and therefore they return every year, no matter how thoroughly you cleaned last year. You can read more about the timing of the algae treatment itself in the guide on algae treatment in spring or autumn.

When is cleaning not enough?

When decking is grey, rough and splintering, the problem is a weathered surface rather than dirt alone. Cleaning removes algae and deposits but cannot remove wood damaged by UV exposure. If the grain is raised or the old oil is flaking, the deck needs sanding back to sound wood before it is oiled again.

We see this particularly on balcony decks in Aarhus Ø. At Isbjerget, Z-huset and Nicolinehus, decks are close to the water and exposed to strong winds, salt-laden air and shade from neighbouring buildings. The wood stays damp for longer than decking in a sheltered garden, so a soap wash may be insufficient and balcony deck sanding may be needed. If you want to restore the colour, read our guide to grey wooden decking and our guide to sanding balconies and wooden decks.

What determines the price of professional cleaning?

The price is determined by five factors: floor area, wood type, how degraded the surface is, accessibility, and whether the deck only needs cleaning or also sanding and oiling. A hardwood balcony on the 8th floor with elevator access does not cost the same per square metre as a pine deck in a residential garden.

We provide a fixed price for the job before work begins, so you don't get a bill based on time spent, and we respond to your inquiry within 24 hours. The work is covered by our workmanship guarantee. Call 20 98 88 11 or get a fixed price for your deck.

Should the deck be oiled after cleaning?

Yes, if you want the colour to last. Cleaning removes algae and dirt, but leaves the wood unprotected against UV and water. The deck must be dry all the way through before the oil can penetrate. Softwood like pine and spruce typically needs oil every year, hardwood often less frequently.

In comparison, we typically re-treat an oiled wooden floor indoors every 1-2 years, and outdoors, the wood is exposed to rain, frost, and sun all year round. Pigmented oil protects better against UV than clear oil, but also changes the shade, and we review the choice in the guide on which deck oil you should choose. The actual workflow is in the guide to oiling the deck, and if you want to take it off your calendar, it can be fixed with our oil maintenance plan.

Frequently asked questions

Written by

Øens HåndværkerCentral

We sand and surface treat floors, stairs, balconies, wooden decks, and worktops - based in Aarhus Ø and with projects throughout the country. You get a fixed price before work begins and a workmanship guarantee on the work performed.

Read more about us