Wood Restoration
When starting a wood restoration project, preparation is key. Wood exposed to the elements often accumulates dirt, grime, algae, mold, and other surface growth. The first step is to clean the wood. 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.
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
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.
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:
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
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.
From here, there are two options:
Wait around an hour for the biocidal cleaner to work at maximum efficiency. Then wash it off with a water hose.
For a superior shine and to really bring weathered wood back from the dead, we recommend the use of an Oxalic Acid-based Wood Scrub.
If you’re opting for the full treatment, leave Roxil 100 Wood & Patio Cleaner on for at least 15 minutes. (For best results with extreme grime, leave for 24 hours) Resume scrubbing with a stiff brush.
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.
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. If using sandpaper alone, use a grade of around 220 grit for best 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.
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.
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.
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