How to Clean Decking and Patios Using a Power Washer

Using a power washer is an excellent way to clean up decking, patios, drives and other hard standing surfaces. Today power washers are not expensive to purchase a basic model, some are as low as only £50 and can be used also on the external masonry of your house to wash away algae etc., and of course, to clean the car!!

Over time patios and decks will accumulate algae, lichen and moss throughout the course of the year and when they do they become slippery and dangerous if not cleaned.

Why Power Wash Decking and Patios?

Maintaining your outdoor spaces like decked areas and patios is crucial for preserving their beauty, durability, and safety.

Over time, dirt, grime, algae, and mildew can build up on these surfaces, leading to discolouration of the timber, slippery patches where algae accumulates, and even long-term damage such as rot and decay.

Regular cleaning, especially power washing, can keep your deck or patio looking pristine and extend its lifespan by numerous years in some cases. Here are some of the main benefits:

• Restores Appearance: Outdoor surfaces are constantly exposed to the elements and over time, this causes dirt, mould, algae, and mildew to build up. Power washing gives a deep clean, stripping away all of this accumulated grime and restoring the deck or patio to its original state.
• Prevents Long-Term Damage: Dirt and organic matter, such as mould and algae, can cause considerable damage over time. As timber is very porous it can absorb moisture when not cleaned regularly, leading to rot or warping. Similarly, concrete patios, pavers etc. can become cracked, stained and slippery when algae, mildew and the likes are allowed to sit for long periods.
• Increases Safety: Safety is an important consideration. Due to exposure, moss, algae and mildew grow and make surfaces very slippery, especially in the wet. By power washing such surfaces, it is removed and no longer poses a risk.
• Cleans in Preparation for Staining/Sealing: If you are needing to stain or seal your deck, it’s essential to thoroughly clean it as such coatings don’t adhere when applied to mould or mildew and if done so will fail very quickly. Power washing removes this back to the original timber surface ready for successfully treating.
• Environmentally Friendly: Power washing is also a much more eco-friendly option compared to using harsh chemicals or scrubbing by hand!
• Saves Time and Effort: Scrubbing is extremely labour-intensive and time-consuming, however by contrast, power washing is much faster and also often much more thorough.

How do you Prepare for Power Washing Decking or Patios?

As we have touched on above, to ensure the success of any staining or other treatments for timber decking or indeed cleaning down a patio, preparation is one of the key factors. To ensure it is done correctly, work through the following steps:

Step 1 – Clear the Area

Before you start power washing, you need to remove all furniture, plants, BBQ’s and other items from the area.

As power washing involves spraying water at high pressure, which can easily knock over or damage anything left on the surface anything moveable needs to be shifted well out the way.

Additionally, clearing the area allows full access to all corners, edges, cracks etc.

Finally, make sure to also sweep away loose dirt, leaves, and debris and anything else that could easily stick once it becomes wet.

Step 2 – Inspect for Damage

Next, check your decking or patio for any signs of damage before you start power washing. This can include things such as loose boards, cracks in the wood, or damaged slabs.

Pressure washing can sometimes exacerbate these issues, especially if the water is applied at high pressure.

Fixing loose boards, filling cracks, or replacing any damaged slabs beforehand will prevent further deterioration and ensure the water doesn’t seep into unwanted areas, causing additional damage.

For decking, look for signs of rot or splintering. For stone or concrete patios, check for cracks or erosion that could be worsened by the high-pressure water.

Step 3 – Cover Immovable Vegetation and Nearby Objects

If your deck or patio is near plants, shrubs, or delicate landscaping, it’s important to protect them from the force of the water and any cleaning solutions you plan to use.

To do so, cover plants with plastic sheeting or tarps to shield them from the spray. Additionally, if there are any walls, windows, or doors close to the area, consider covering these with drop cloths to prevent accidental damage or water splashes.

Step 4 – Choose the Right Cleaning Solution

While using plain, good old water can often remove a good deal of dirt and grime, for tougher stains, mould, or mildew, you might need to also use a cleaning solution.

Be sure to choose a cleaning product that is specifically designed for the type of surface you’re washing, whether it’s wood, composite, stone, or concrete.

Eco-friendly and biodegradable cleaners are highly recommended, as you can be sure they won’t harm your plants or the environment.

If you’re working on wood, avoid bleach-based cleaners, which can strip the wood’s colour and weaken its structure.

Make sure to follow the manufacturer’s instructions for mixing and applying the cleaning solution, and use the recommended pressure settings for your specific surface type when cleaning over after application.

Setting up a Pressure Washer Correctly

Another very important step when power washing is to ensure that you have setup your power washer correctly so that it cleans as it should but does not produce a spray so powerful that it also causes damage.

With this in mind, before you start cleaning the entire deck or patio, it’s essential to test the pressure washer on a small, inconspicuous area first to ensure that the pressure setting is correct.

Different materials can handle different levels of pressure. Too much pressure can damage wood fibres, chip concrete, or loosen pavers, while too little pressure may not effectively clean the surface.

To allow for all the pressure variations required for cleaning different objects, pretty much all cleaner lances feature an adjustable nozzle that can be set to produce different strength water jets.

A little experimentation may be required to find the right setting and balance between cleaning power and surface protection.

For wooden decks, using a wide-angle nozzle (typically 40-60 degrees) is advisable, while concrete and stone patios may require a more concentrated spray.

Pressure Washing Techniques

Once you have setup your pressure washer correctly, before you actually start cleaning, it’s also important to note that there is a particular technique to using a pressure washer to ensure that you get the best level of cleaning, whilst ensuring no damage is caused.

To ensure this is the case, adhere to the following 3 golden rules:

• Go with the grain: Power wash with the grain and not against it as this will cause damage if you don’t.
• Keep nozzle at even distance: The distance you hold your nozzle will depend on what you are working on so you may need to experiment to get it spot on, however a good rule f thumb is around 6 inches, but always start far away on a small, inconspicuous area and work in.
• Keep nozzle moving: Don’t dwell too long in one place as the concentrated pressure can cause large amounts of damage.

What Do You Need for Power Washing Decking and Patios?

To power wash your decking or patio effectively, you’ll need a few essential items, starting with the power washer itself.

If you don’t already own one, affordable options can be found at most DIY stores, garden centres, or home improvement shops. While budget models may work for basic cleaning, investing in one with at least 110 bar pressure, a good lance, and portability is key for better results.

Next, you’ll need an outdoor water supply and an RCD-protected power outlet. If you don’t have an outside tap, check out our guide to installing an outside tap. Alternatively, hose adaptors can connect your power washer to an indoor tap.

Make sure your power washer is connected to an electrical supply with an RCD plug for safety. This will shut off power if any faults are detected, protecting you from electrical hazards.

For cleaning large areas, consider using a Patio Cleaner attachment instead of the standard lance. This tool uses rotating jets to cover more surface area, cutting cleaning time in half.

For best results, use a quality anti-fungal wash to pre-treat the surface. Products like Everbuild Fungicidal wash help break down algae and lichen, making them easier to remove with the power washer.

Lastly, this is a wet and messy job, so wear old clothes, sturdy boots, and safety gear like gloves and eye protection when working with chemicals.

How to Power Wash Decking

Now that you know exactly what you need in order to successfully clean your patio, decking or hard standing area it’s now time to get to work.

For the purposes of this example we are going to be cleaning down some decking that has been left for a long time and is suffering form heavy algae and lichen build-up.

Step 1 – Treat Decking/Surface with Anti-fungal

Before power washing, apply an anti-fungal treatment to tackle heavy algae and lichen build-up. Skipping this step might leave stubborn lichen embedded in the wood, making the power washer less effective. Pre-treatment helps loosen the algae and lichen, ensuring a deeper clean later.

Follow the manufacturer’s instructions for your chosen surface and treatment. We recommend using Everbuild Fungicidal Wash, which can be applied with a brush or a low-pressure garden sprayer for even coverage.

Let the solution sit for 20-30 minutes to break down the build-up. Then, use a stiff brush to scrub the surface, making sure to get into the grooves of the decking. You’ll notice the grime lifting as you work, revealing a cleaner surface underneath.

Though it’s a tough job, this step is essential for restoring your decking to as good a condition as it possibly can be.

Step 2 – Set Up Your Power Washer

After treating and scrubbing the surface, it’s time to set up your power washer for cleaning.

Position the power washer near your starting point. If the high-pressure hose isn’t attached, connect it to the main unit using the screw-on or push-and-twist mechanism. Then, connect the gun to the other end of the hose and attach the lance to the gun.

Next, connect a hose from your water source (e.g., an outdoor tap) to the water inlet on the power washer.

Plug the power washer into an outdoor socket or extension cable, using an RCD plug for safety. Turn on the water, power up the washer, and test it.

Whilst testing, also setup the nozzle so that it produces the correct strength spray for the object you are working on. As we have stated, before starting properly, test the nozzle strength on a small, inconspicuous area first.

Once confirmed, turn everything off until you’re ready to start cleaning.

Step 3 – Power Wash the Decking

When you’re ready, turn on the water supply first, then the power washer. Never start the washer without water running through it, as this can damage the pump.

Hold the lance nozzle about 6 inches from the decking at first and pull the trigger. The washer will activate, sending a high-pressure water jet from the nozzle.

Work in small sections, focusing the water jet on areas with build-up. Adjust the nozzle distance to find the best cleaning effect, either moving closer or further from the surface as needed.

Continue methodically over the entire surface to remove all dirt, algae, and lichen.

After cleaning, rinse the entire area with the power washer to clear away any dirty water. Leaving it behind can encourage algae and lichen to return quickly.

Step 4 – Oil and Treat Decking

After cleaning your decking, protect your hard work by preventing future algae or lichen growth.

While some regrowth is inevitable, you can significantly reduce it by applying a high-quality decking oil or treatment. These products penetrate the wood, creating a protective seal that helps block moisture and limits algae and lichen build-up.

For best results, apply the treatment annually to keep your decking in excellent condition. Regular maintenance ensures long-lasting protection and keeps your decking looking great year-round. For detailed instructions, check out our full guide on treating timber decking here.

How to Power Wash a Patio

Now that we’ve covered power washing decking, let’s focus on patios.

Patios, like decking, can accumulate algae, lichen, and other surface build-up, especially during colder months. If left untreated, this growth can make the surface slippery and hazardous, which is why it’s essential to keep patios and other hard surfaces clean and free from debris and lichen.

Step 1 – Clean the Patio Joints

Before power washing, start by cleaning the joints between the patio slabs.

Use a patio scraper, cleaning hook, or block paving cleaner to remove any debris, weeds, or plant growth from the joints.

After clearing the joints, sweep up and dispose of the waste.

Step 2 – Apply Brick and Patio Cleaner

Next, apply a cleaning solution to the patio, similar to how we treated the decking. For this, we’ll use Everbuild 401 Brick and Patio Cleaner, which contains muriatic acid. Please note: Muriatic acid is dangerous!

Always wear old clothes, thick rubber gloves, eye protection, and a respiratory mask. The fumes are toxic and can severely harm your respiratory system.

If you prefer a gentler alternative, you can use fungicidal wash, though it won’t be as effective as the brick and patio cleaner.

Pour the cleaning solution into a plastic bucket (avoid metal buckets as the acid reacts with metal). Use a stiff scrubbing brush to apply the solution, scrubbing small sections of the patio. The acid works quickly to lift surface growth.

Continue scrubbing the entire patio, working methodically, and leave the solution on the surface for 20-30 minutes to take effect.

Step 3 – Power Wash the Patio Surface

After the Brick and Patio Cleaner has worked its magic, it’s time to use your power washer. The cleaner will have loosened the dirt, lichen, and algae, making it easier to wash away.

Move methodically across the patio, using the power washer to blast off any remaining debris. Direct the waste water towards the nearest drain for easy clean-up.

Once you’ve cleaned the entire patio, you’ll be left with a fresh, revitalised surface that looks like new.

Using a patio cleaning attachment with your power washer can save time and effort. While some washers come with one, you can buy a separate attachment for around £50 if needed.

For patios that haven’t been cleaned in years, a second round of cleaner and power washing might be necessary to remove all build-up.

Be cautious when using high pressure on delicate surfaces, as too much force can damage patio slabs. Also, the muriatic acid in the cleaner is diluted by the time you wash it off, making it safe for drains and soil.

Power washing your decking or patio is essential for maintaining its condition and ensuring safety, especially during colder, wetter months when surfaces can become slippery and hazardous.