How to Clean and Restore Decking - Complete UK Guide

Your deck takes a pounding from the British weather. Rain, frost, UV and foot traffic turn honey-coloured timber grey within a couple of years, and moss loves the damp corners between boards. The good news is that most decks come back to life with one weekend of work. You don't need to replace the timber, and you don't need expensive kit. You need the right cleaner, a decent brush, and a bit of patience while it dries.

This guide walks through the whole job from start to finish: what to buy, how to clean the boards properly, how to bring grey wood back to its original colour, and how to protect it so you don't have to repeat the hard part next year. It's written for UK gardens, which means it covers the damp-shade moss problem that most American guides simply ignore.

Before you spend a penny, check the forecast. The single biggest mistake people make is cleaning decking before a week of rain. The cleaner needs time to work, and the wood needs two or three dry days afterwards before any oil will take. Pick a dry stretch, and the rest of the job is straightforward.

What You Need to Clean Decking

The shopping list is shorter than you think. For a typical 20 square metre deck you need a stiff-bristle brush, a bucket, and a decking cleaner. A pressure washer helps on big decks but is optional, and you only need oxalic acid if your boards have gone grey. Here's what we recommend, all checked live on Amazon UK.

Step-by-Step: How to Clean Your Deck

Step 1: Clear and sweep

Move every plant pot, chair, table and BBQ off the boards. Give the whole deck a good sweep to remove leaves, grit and loose dirt. Grit is the sneaky one - if you scrub over it, you're basically sanding the deck with whatever was stuck under the furniture. If you have planters sitting directly on the boards, check underneath for trapped moisture and blackened wood. That's a sign you need to raise them on feet before you reassemble.

Step 2: Treat moss and algae

For decks with visible green growth, apply a bleach-free outdoor treatment before you scrub. Wet & Forget Mould, Lichen & Algae Remover goes on with a watering can or sprayer and gets left for 15 to 30 minutes. You'll see the green start to lift and turn brown as it dies. This step makes the scrubbing dramatically easier - you're removing dead growth instead of fighting live moss that's rooted into the grain.

Step 3: Scrub along the grain

Now the physical bit. Use a stiff-bristle deck brush and scrub along the grain of the boards, never across it. Across the grain you'll leave permanent scratch marks that hold dirt. Work in small sections, rinse as you go, and keep the brush moving. For stubborn patches, a scrubbing brush with a long handle lets you put your weight behind it without kneeling.

Step 4: Pressure wash (optional but effective)

A pressure washer cuts the job time in half on a big deck, but you have to treat timber with respect. Set the machine to low pressure, under 100 bar, fit a wide fan nozzle, and hold the lance at least 30cm from the boards. Spray along the grain and keep moving - lingering on one spot with a narrow jet will gouge softwood. If your machine only has a turbo nozzle, don't use it on decking and use the brush instead.

For the full lowdown on which machine suits which job, read our Best Pressure Washers UK 2026 roundup, or our dedicated guide to pressure washing patios and driveways.

Step 5: Bring grey wood back with oxalic acid

Here's the step most guides skip, and it's the one that makes the biggest visual difference. If your boards have gone silvery grey, that grey isn't dirt - it's the surface fibres of the wood broken down by UV and rain, and scrubbing won't shift it. Oxalic acid lifts that weathered layer and restores the natural honey colour underneath. It's the same trick professional deck restorers use, and it's cheap.

Step 6: Rinse and let it dry completely

Rinse the whole deck thoroughly to wash away every trace of cleaner and loosened grime. Leftover cleaner under a coat of oil will react and leave blotches. Then leave the deck to dry for at least 48 hours, ideally with a couple of dry days in a row. Wood needs to be properly dry before any treatment will soak in. You'll know it's ready when the boards feel dry to the touch and look lighter than they did when wet.

How to Protect Your Deck After Cleaning

Cleaning is only half the job. An unprotected deck will be grey again within a season. A coat of decking oil soaks into the timber, feeds it, and forms a water-repellent barrier that stops moisture sitting in the grain where moss takes hold. Most UK decks need one coat a year, applied on a dry day when the wood is fully dry.

If you'd rather have a richer, deeper colour that lasts longer between coats, the Ronseal Ultimate Protection Decking Oil is a step up. It contains extra UV filters and a water repellent that keeps rain beading on the surface, and it holds its colour noticeably longer than standard oil. It costs more per tin, but on a deck that gets full sun all day it's worth it.

One common question is whether to oil or stain. Oil is the right call for most people. It's forgiving to apply, doesn't peel, and a fresh coat each year keeps the deck healthy. Stain gives you solid colour options and longer wear, but when it fails it peels and has to be stripped before you can reapply. If you want the natural wood look, oil wins every time.

How Often Should You Clean Your Deck?

Once a year, in late spring or early summer, is right for most UK decks. That's the sweet spot - the worst of the winter moss is visible, the weather is warm enough to dry the boards, and you get the whole summer of use from the clean and re-oil. Decks in heavy shade, or under trees, may need a second lighter clean in autumn. More than twice a year is overkill and just strips the oil you applied.

A few small habits between annual cleans keep the deck looking good. Sweep it once a fortnight to stop leaves breaking down into stain. Move plant pots around every couple of months so the boards underneath don't stay damp. And deal with moss the moment you see it - a patch treated early takes five minutes, while a deck left for a year takes a full weekend.

Frequently Asked Questions

Products Mentioned in This Guide

If you're setting up your garden toolkit from scratch, our Essential Home DIY Tools guide covers the basics every homeowner needs, and the garden fence painting guide shows how to keep the rest of your timber looking sharp too.

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Last reviewed: July 31, 2026 · Evidence-based content · Contains affiliate links