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How to clean a garden shed

Wood Restoration Project: Shed

When starting a wood restoration project, preparation is key. Any wood that has been exposed to the elements for an extended period of time will have built-up dirt, grime, algae, mould or other biological growth on its surface. The first step of any outdoor wood restoration project is to clean it all off prior to further treatment. Dirt, debris and grime can prevent wood finishes from adhering to wood properly, leading to an uneven finish and reduced effectiveness. 

We’ve restored a shed to illustrate this guide, but the principles hold for any type of outdoor furniture. Follow these steps to effectively and easily clean fences, furniture and decking prior to applying a protective wood treatment. 

There are 3 main steps to properly preparing outdoor wood like furniture and decking for fresh treatment:

Cleaning Preparation

Before you start, here are the things you’ll need:

To clean the wood, start by brushing away dry debris:

  • Leaves
  • Twigs
  • Dirt and dust
  • Moss and algae
  • Any other organic growth that may be causing discolouration
A contractor cleans away debris prior to biocidal cleaning
Removing Debris
Always work in the direction of the wood grain.
A Contractor Continues To Clean Away Debris From A Shed
The right tools for the job
A stiff-bristled brush is essential.

Working in the direction of the wood grain, use a stiff-bristled brush or broom to scrub the surface of the wood. The aim here is to remove as much loose debris as possible until there’s nothing left on the wood except surface staining and biological growth. Don’t be afraid to put some elbow grease into it to lift stubborn caked-on mud and algae. Once you’ve removed as much dirt as possible from the entire structure, the wood surface should be bare wood. Keep in mind, at this point there may still be some staining visible on the wood’s surface. Medium to extreme mould and algae growth will be near-impossible to lift using a brush alone.

Now you’re ready for a biocidal wash.


Washing timber with biocidal cleaners

Outdoor timber is a breeding ground for mould and algae. Water and elbow grease makes your outdoor furniture and decking look clean, but invisible algae spores may still be present on the surface. They wait in hiding for the right conditions for growth: high humidity levels and lots of moisture. The threat of biological growth can only be properly ruled out with a biocidal cleaner. 

Biocidal wood cleaner benefits:

  • Non-abrasive cleaning
  • Quick action
  • Fully removes mould and algae
Laying a ground sheet prior to biocidal cleaning
Protect your greenery
A plastic sheet helps keep your lawn and flowers in tip-top condition.

Plant Protection Tips

Biocidal cleaners are very effective at removing mould and algae growth that has become embedded into the wood’s surface.

Ensure that biocidal cleaners do not accidentally come into contact with flowers, vegetables, other garden plants or the lawn.

Here are some must-follow tips for protecting plants during biocidal treatment:

  • Use a thin plastic sheet to shield plants from contact
  • Minimise splashback by using a fine spray instead of a wide spray
  • When rinsing make sure to divert the run-off away from plant life

How to apply biocidal cleaners to outdoor timber

A contractor loads his pressure sprayer with Roxil 100 Wood & Patio Cleaner
Pump it up
Pump-action sprayers are the most efficient way of consistently treating a large surface.
Roxil 100 Wood & Patio Cleaner sprayed on a shed
Slow & Steady
Pump-action pressure sprayers deliver even coverage

Most biocidal cleaners can be applied by brush, roller or spray—however, this depends on liquid consistency. Algae-saturated wood may go brown or black following application – don’t worry, this is a sign that the biocide is doing its job. 

For this shed project, we used a 5-litre can of Roxil 100 Wood & Patio Cleaner. For the most consistent and even application, we recommend decanting your chosen biocidal cleaner into a pump-action pressure sprayer. For Roxil 100 Wood & Patio Cleaner, apply 1 litre per 5㎡ timber.

Before using your pressure sprayer, ensure the screw cap is fully closed.

When using a pump-action pressure sprayer, always spray in the direction of the wood grain to ensure that the biocide fully absorbs into the wood. Spray slowly and steadily to ensure maximum coverage and to avoid overspray and splashback.

After use, thoroughly clean the tank and the nozzle to avoid future clogging.

Leave Roxil 100 Wood & Patio Cleaner on for at least 15 minutes. For best results with extreme grime, leave for 24 hours. Then proceed to rinsing.

How to rinse biocidal cleaners from outdoor timber

Rinsing with a garden hose
The lower the pressure, the better
We recommend a simple garden hose to wash off any biocidal cleaner.

Use a garden hose to wash away biocidal cleaner.

In cases of extreme biological growth, thick lichen growth may still be embedded into the surface following rinsing. Use a firm abrasive brush to lift lichen from the surface and clear away any loose debris. 

You can use a pressure washer to clean wooden decking and furniture, but be careful. Power washing is destructive and timber is comparatively delicate. The sheer volume of water used in pressure washing combined with the vulnerable nature of untreated wood risks damage. Remember—unprotected wood expands and contracts in water. We want to minimise the splitting risks as much as possible. For these reasons, we do not advise using a pressure washer to clean outdoor wood.

Always use the lowest-pressure setting to avoid damaging the wood fibres. Aim the spray in the direction of the wood grain. Be careful—the higher pressure of the sprayer may cause biocide and contaminated water to splash onto flowerbeds and accidentally cause damage. 

Always allow the wood furniture or structure to dry completely before moving on to the next step.

Does your shed still look greyed, weathered and generally tired? If so, for a superior shine and to really bring weathered wood back from the dead, we recommend using Roxil Wood Scrub Gel after the biocidal treatment has been fully removed.

How to use Roxil Wood Scrub Gel

While still damp, apply a generous layer of the gel using a brush or roller, following the direction of the wood grain. 

For best results, leave the gel on the shed for an hour. If you’re in a hurry, keep in mind that Roxil Wood Scrub Gel needs at least 30 minutes to work its magic.  The wood noticeably lightens as the gel begins to work.

Roxil Wood Scrub Gel Application on a shed
Shedding the grime
Roxil Wood Scrub Gel is the ultimate wood reviver.

With a stiff brush, scrub the gel layer over the surface of the wood in the direction of the grain.

Keep wetting with water to aid the gel’s workability. Thoroughly rinse the surface and allow to dry.

Do not use a pressure washer after a Roxil Wood Scrub treatment, as the revived softwood is vulnerable before it is preserved and protected.

Clean any excess from the brush with warm soapy water.

Your shed is now fully cleaned. All that’s left is to smooth the surface and then it’s on to Preserving and Protection.

How to denib wood 

Now that all cleaning treatments have been washed off and the wood has dried, you may notice a residue across the surface similar to in the image on the right. This textured surface is raised wood grain. Untreated wood is absorbent. When we treated the wood with water-based cleaner, the outer layer of wood fibres swelled slightly in response to the increased moisture levels.

Once the oxalic acid treatment has been fully removed and the wood surface has dried, it’s time to denib using sandpaper or a foam-backed denibbing pad. A sandpaper grade of 60-100 grit will give the smoothest most consistent results.

Make sure to mask up and wear protective goggles – as we’re going to be sanding very finely, there is a chance that small wood particles may circulate the area.

The denibbing process
A light & steady hand
Denibbing is the lightest type of sanding you can do. Be gentle!

Following the wood grain, apply light pressure to the wood with the denibbing pad until the residue has been taken away. “Gentle” is the operative word here, you barely need to apply pressure at all. Always denib in the direction of the wood grain – one way only!

Take extra care to only denib one way – no back-and-forth motion allowed! Just one or two light passes are needed to remove the wood residue. 

If the denibbing pad gets clogged with sawdust, direct the pad away from you and shake it to dislodge trapped sawdust.

When you’re finished, the surface should be smooth to the touch with little to no imperfections.

Smooth surface after denibbing process
Smooth & Clean
The beautiful end results.

You should denib everywhere you applied the biocide – this may take some time but it’s well worth it for smooth and clean results. A smooth surface will also help adhesion for the next stage.  

Once you’ve denibbed, congratulations! Your shed, furniture or fence is now ready for the next step: wood preservation.

Find out how to strip paint, varnish, wax and other finishes from outdoor wood here.

For more information call
01403 210204