Do not strip the timber. Buy a Kärcher K4 WCM Flex eco!Booster Home so you can turn the pressure down, stand back, and use a wide fan or a T 5 on the high setting. The dirt blaster stays on the hook. We would rather you leave a little film than raise the grain and own a fuzzy deck that holds more algae next year.
Softwood, hardwood and composite all mark if you treat them like concrete. Distance does more than another 20 bar. With the grain, further back than you think, keep moving. If you use the hood, raise the jets and do not lean on the handle. Soap lifts green film. Extra punch planes the board.
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If the deck is a small balcony and you already own a working K4 or K5, buy the T 5 and a bottle of wood cleaner. Do not buy another washer. No outdoor socket? A battery gun can rinse furniture. It is a poor way to wash a green 4 × 5 m deck. First-use distance sits on how to use a pressure washer. The head itself is on the patio cleaner page.
Quick picks
Best overall
Kärcher K4 WCM Flex eco!Booster Home
£229
Max 130 bar Home kit with a T-Racer in the box.
Best if you already have a head
K4 Power Control Flex
£169
Same pump, no T 5. Buy the bare Flex if the head is already in the shed.
Best head for timber
Kärcher T 5
From about £55
Height-adjustable jets. Use the higher setting on wood. Keep it moving.
Best detergent
Kärcher 3-in-1 wood cleaner
£8.99 at Trafalgar
1 L Plug ‘n’ Clean bottle for treated and untreated outdoor timber. Soap does more than extra bar.
Comparison table
| Model | What it is | Why it is on this page | Typical UK price (22 Aug 2026) |
|---|---|---|---|
| Kärcher K4 WCM Flex eco!Booster Home | 130 bar washer + T 5 | Default deck kit. Turn the Vario down. Raise the head. | £229 |
| K4 Power Control Flex | 130 bar washer, 8 m Flex | Same pump if you already own a T 5 | £169 |
| T 5 | Clip-on head | Higher jet setting for timber | From about £55 |
| 3-in-1 wood cleaner | 1 L detergent | Green film. Low-pressure apply, then rinse | £8.99 at Trafalgar |
A K5 will wash a deck if you turn it down. Buy one for a long drive, not because timber needs 145 bar.
Fan, distance, keep moving
A close rotary jet raises the grain, stripes the boards and leaves a deck that then holds more algae. That is the whole failure mode. Wide Vario, with the grain, start further back than you think. Only close in if a hidden test patch stays honest. If the surface furs, stop and finish with a hose and a deck brush.
Composite is not timber. Check the board maker. Many UK ranges allow a low-pressure fan rinse and forbid a pencil jet. If the booklet is missing: wide fan, 30 cm or more, with the boards, no rotary, no bleach. Do not fire into the gaps. Water forced under the boards sits on the joists.
Kärcher K4 WCM Flex eco!Booster Home
The deck kit if you do not already own a mains washer
- Buy: Amazon Home listing £229 · Kärcher UK Home
- Pressure / flow: 20 to 130 bar, 420 L/h
- Hose: 8 m PremiumFlex
- In the box: K4, Power Control gun, Vario, dirt blaster, T 5, 1 L stone cleaner
- Who it is for: households that need a washer and a hooded head, and will treat the deck as a low-pressure job
Home means a T 5 in the carton, not a different pump. The LED on the gun shows the step. Drop it for timber and composite. Open it only if you later do stone. The stone cleaner in the box is for slabs. Buy wood cleaner for the deck. Do not then add a second T 5. The dirt blaster is for stubborn spots on stone, not for the boards.
Eight metres covers a typical UK deck from a corner. If the deck shares a Saturday with a long, green drive, read K4 vs K5 and buy the K5 instead. The extra flow is for the stone, not the timber. Turn it down when you step onto the boards.
Skip it if you already own a working K4 or K5. Buy the T 5 and the wood cleaner. Skip it if the boards are already rotten. A washer will find the soft spots.
Kärcher K4 Power Control Flex
The bare machine if the T 5 is already in the shed
- Buy: Check latest price £169
- Pressure / flow: 20 to 130 bar, 420 L/h
- Hose: 8 m PremiumFlex
Same pump, same gun, no head. Buy this if a Home box would give you a second T 5 you will not use. On timber the Vario is the safe default. A K2 will rinse a table. It is a poor deck machine: short hose, air-cooled motor, 110 bar you cannot always turn down as cleanly. That comparison is K2 vs K4.
Skip it if you need the head as well. The Home kit is then the rational box.
Kärcher T 5 T-Racer
The head that makes a deck less stripy
- Buy: Trafalgar from about £55 · Screwfix £58.99
- Compatible with: K2 to K7
The height adjustment is why this head is on a decking page. Hard stone wants the closer setting. Timber wants the higher one. Keep the brim flat and moving. Park it in one spot and you will raise a ring of grain. Do not chase silvered boards until they are raw. You are lifting film, not planing the deck. The T 7 Plus is overkill for most timber.
Skip it if you do not own a Kärcher, or a Home kit is already in the basket.
Kärcher 3-in-1 wood cleaner
The bottle that does more for green film than another 20 bar
- Buy: Kärcher Centre Trafalgar £8.99
- Size: 1 L Plug ‘n’ Clean
- Who it is for: treated and untreated outdoor timber
Soap is a low-pressure job. Fit the bottle, twist the Vario to the detergent setting, apply, wait, then rinse on a wide fan. High-pressure soap wastes cleaner and sends foam into the drain. Do not put stone cleaner on timber because it came in a Home box. Do not put deck cleaner on a car. Bleach on composite is a common way to void a warranty and bleach the lawn.
Skip it if the only dirt is loose dust. A plain rinse on a wide fan is then enough.
What the dirt blaster is for
Stone, not timber. The same jet that lifts moss from concrete will chew a board in a few seconds. If a stain will not move on a wide fan and soap, it is a brush job or a replacement board, not a reason to click the rotary on. A patio and a drive can take more punch. Decking cannot. Petrol is the wrong tool here.
How to choose
- Own nothing, timber deck, tap and socket. Kärcher K4 WCM Flex eco!Booster Home. Add wood cleaner. Leave the dirt blaster on the hook.
- Already own a K4 or K5. T 5 on the high setting, plus wood cleaner.
- Already own the head. Bare K4 Flex.
- Long drive as well as the deck. K5, turned down on the timber.
- No socket. Cordless rinse, then a brush.
FAQ
What is the best pressure washer for decking in the UK right now?
A Kärcher K4 WCM Flex eco!Booster Home, used on a wide Vario or a T 5 on the high setting. 130 bar you can turn down is the useful class. The dirt blaster is not part of the job.
Will a pressure washer damage decking?
Yes, if you stand close, use a rotary jet, or park a patio head in one spot. Wide fan, distance, keep moving. Soap and a brush do more for algae than extra bar.
Can I use a K5 on decking?
Yes, if you turn it down. Buy a K5 for a long drive or a large patio, not because the boards need 145 bar.
Do I need a T 5 for a small deck?
No. A wide Vario and patience will do a 2 × 3 m balcony. The head earns its keep on a larger deck where striping from a lance is the daily frustration.
Can I use the dirt blaster on a stubborn stain?
No. That is how you rip the grain. Soap, dwell, wide fan, then a deck brush.