If you've picked up a bottle of Patio Magic concentrate and you're staring at the label wondering exactly how much water to add, you're not alone. Getting the dilution right is the single biggest factor in how well this patio cleaner performs, and it's also the step most people get wrong. Too weak and you'll be disappointed by the results; too strong and you're wasting product without making it any more effective. This guide walks through exactly how to dilute and mix Patio Magic concentrate, why the ratio matters, and how to use it correctly once it's mixed, including on concrete.
Why Dilution Matters in the First Place
Patio Magic's concentrate bottles, the 5L and 2.5L sizes, are formulated to be mixed with water before use. The active ingredient is benzalkonium chloride, present at 5-10% w/w in the concentrate (the 2.5L label states 7.5% w/w, or 75g per litre), alongside a small amount of ethoxylated C9-11 alcohols. That's a strong active concentration, which is exactly why it needs diluting properly rather than applied straight from the bottle. Diluting it correctly spreads the active ingredient across enough liquid to treat a large area evenly, and brings the concentrate down to a strength that's effective against green algae, moss, lichen and green or black mould staining without being wasteful.
It's worth flagging early that not every Patio Magic product needs this step. The Patio Magic Ready To Use Spray 5L comes pre-mixed and is ready to spray straight from the bottle, so if you'd rather skip mixing altogether, that's the option to reach for. But if you already have, or are considering, the 5L or 2.5L concentrate, understanding how to mix it is what determines whether you get the results you're expecting.
How to Dilute Patio Magic: The Two Ratios
There are two dilution ratios to know, and which one you use depends on how bad the algae, moss or mould problem actually is. For a normal infestation, meaning visible green algae, moss or black staining that's had time to establish, dilute 1 part Patio Magic to 4 parts water. For a light, early-stage infestation, where the surface is only just starting to show a green tinge or the first signs of mould, a weaker mix of 1 part Patio Magic to 9 parts water is enough. The lighter mix goes further and is a gentler treatment, which makes sense if you're catching the problem early or treating a surface as routine maintenance rather than a heavy clean.
| Infestation Level | Dilution Ratio | Best For |
|---|---|---|
| Normal | 1 part Patio Magic : 4 parts water | Established green algae, moss, lichen, black mould staining |
| Light | 1 part Patio Magic : 9 parts water | Early-stage greening, routine maintenance treatments |
As a rough guide for how far this goes once mixed, roughly 1 litre of diluted solution covers 3-7m² of surface, depending on how porous the surface is and how heavily you apply it. That means the 2.5L concentrate bottle makes up to 85m² of usable diluted solution, and the 5L bottle stretches to up to 170m², which is worth factoring in when you're working out how much you need for a driveway, path or full patio area.
Mixing It Properly: Step by Step
The mixing process itself is simple, but a few small habits make a real difference to how evenly the product ends up applied. Start with a clean watering can or a garden pump sprayer, whichever suits the size of the area and how precisely you want to apply the solution. A watering can with a fine rose suits smaller patios and paths, while a pump sprayer gives more control over larger driveways or vertical surfaces like garden walls.
Measure your water first, then add the concentrate in the ratio you need, rather than the other way round. Adding concentrate to a container and topping up with water by eye is where a lot of over- or under-dilution happens, because it's easy to misjudge the final volume. A marked measuring jug for the concentrate, and a watering can or sprayer filled to a known volume line for the water, takes the guesswork out of it. Give the mixture a gentle stir once both parts are in so the concentrate is evenly distributed rather than sitting in a stronger layer at the bottom.
One detail that catches people out: mix only what you're going to use straightaway. Patio Magic should be applied to the surface as soon as it's diluted, not pre-mixed in a batch and left in a shed for next weekend. The diluted solution is meant to be used fresh, so plan your mixing around the day you're actually treating the surface, ideally checking the weather first so you're not caught out by rain.
Common Mixing Mistakes to Avoid
A few mistakes come up again and again, and they're easy to avoid once you know what to look for. The first is guessing the ratio instead of measuring it. Eyeballing "roughly a quarter concentrate" might feel close enough, but small errors compound over a full watering can or sprayer tank, and you'll end up either under-treating a heavy infestation or using far more product than a light one actually needed.
The second is using the wrong ratio for the job. If you apply the light 1:9 mix to a driveway that's thick with established moss and black mould, the results may be underwhelming simply because the solution wasn't strong enough for that level of buildup, so match the ratio to what you're actually looking at, using 1:4 for anything well established.
The third is mixing near ponds, water features, or drains. Patio Magic is very toxic to aquatic life, so both mixing and applying it should happen well away from any water source, with care taken to avoid runoff reaching drains, streams or garden ponds. Finally, don't rinse or scrub after applying. Once the diluted solution is on the surface, the job is done, it's designed to be left alone to break down the algae, moss or mould naturally rather than being washed off or worked in with a brush.
Using Diluted Patio Magic on Concrete and Other Surfaces
One of the most common questions is whether concrete needs different treatment to block paving or natural stone. It doesn't. Diluted Patio Magic works the same way on concrete driveways and paths as it does on any other hard outdoor surface, including patios, block paving, garden walls, garden furniture and greenhouse glass. There's no special pre-treatment required for concrete beyond sweeping away loose debris, leaves and moss clumps first so the solution can reach the surface itself.
Apply the diluted solution to a dry surface, ideally when there's no rain forecast for the next 5-6 hours, so it has time to work in before being washed away. There's no need to scrub the concrete before or after treatment, and no need to rinse once it's applied. Just apply evenly and let it get on with the job.
What to Expect After Applying
Once the diluted solution has been applied, patience is part of the process. Green algae and mould staining are typically visibly reduced within 2-4 days, while a fuller effect on moss and lichen can take 1-2 weeks, since these take longer to break down than surface algae. There's no rinsing or scrubbing needed at any point, the treated growth simply breaks down naturally and weathers away. Results tend to last several months before regrowth becomes an issue again, worth bearing in mind when deciding between the normal and light dilution ratio for a repeat treatment. It's also worth noting Patio Magic is formulated for algae, moss, lichen and mould rather than weeds; for weeds growing through paving joints, Doff Knockdown Path & Patio Weedkiller is designed for that job specifically.
Safety When Handling the Concentrate
Because this article is specifically about handling and diluting the concentrate, it's worth being clear on the precautions involved. The undiluted concentrate causes skin irritation and serious eye damage, so gloves and eye protection should be worn while handling and diluting it, not just during application. Take care to avoid breathing in any spray mist once you're applying the diluted solution, and wash your hands thoroughly after handling the concentrate or the mixed solution.
Keep children and pets away from the area while you're mixing and applying Patio Magic, and keep them off the treated surface until it's fully dry, which takes around 5-6 hours. As mentioned above, the concentrate is very toxic to aquatic life, so mixing and applying it near ponds, streams or drains should be avoided entirely, along with anywhere runoff could reach a water source.
Getting the dilution right is a small step that makes a real difference to how well Patio Magic performs, whether you're treating a heavily mossy driveway at the normal 1:4 ratio or keeping on top of early green staining with the lighter 1:9 mix. Measure carefully, mix fresh, apply on a dry day, and let it do its work. For the full range, including both concentrate sizes and the ready-to-use option, you can browse the Patio Magic collection to find the right size for your patio, driveway or path.
