What Strength Sodium Hypochlorite for Patio Cleaning

For most patio cleaning jobs, you want a sodium hypochlorite solution of around 0.5% to 1% for general mold, algae, and mildew, and up to 2% for stubborn growths on tough surfaces like concrete. In practical terms, that means diluting a standard 5%–6% household bleach (which is what most store-bought bottles contain) at roughly 1 part bleach to 5–10 parts water. A good starting point for concrete or brick is 1 cup of bleach per gallon of water, which gets you close to a 0.5%–0.6% working solution. For lighter jobs on more delicate materials like sandstone or slate, go even weaker, around 1:20 dilution or skip sodium hypochlorite entirely.

What's actually in the bottle and why it matters

Sodium hypochlorite is just the active ingredient in bleach. Most household bleach you pick up from a supermarket sits at 5%–6.15% sodium hypochlorite, while some trade-grade or horticultural concentrates run at 10%–15%. When people talk about 'sodium hypochlorite for patio cleaning,' they're usually either diluting standard household bleach or buying a higher-strength concentrate to mix down. If you want the best option for your situation, start by choosing the right bleach strength and dilution for your patio material best bleach for cleaning patio. Knowing your starting concentration matters because a 10% product needs double the dilution of a 5% product to hit the same working strength. Always check the label.

Matching strength to your patio material

This is where most people go wrong. They grab the bleach and use the same strength on everything. If you are wondering does pink stuff clean patios, the biggest tip is to never treat all patio materials the same use the same strength on everything. The surface you're treating should completely change how strong a solution you mix. Here's how I break it down by material:

The reason sandstone and natural limestone get special treatment is that blank" rel="noopener noreferrer">chemical cleaners can react with minerals in the stone, leaving disfiguring discoloration that's very hard to reverse. I've seen homeowners ruin sandstone patios by assuming 'it's just stone, it can handle bleach.' It can't. Stick to the lower end of the scale on anything porous or natural, and always do a small test patch in an inconspicuous corner first.

When bleach actually works (and when it doesn't)

Where sodium hypochlorite shines

Sodium hypochlorite is genuinely excellent at killing biological growth. Washing powder can be helpful for lighter dirt and general scrubbing, but it is not as effective as sodium hypochlorite for killing algae and mildew. Algae, green slime, black spot, mildew, and mold all respond well to it because bleach breaks down the cell walls of the organisms rather than just washing them away. On a sealed concrete or brick patio covered in green algae, a proper bleach solution will kill and lift it far more effectively than scrubbing alone. It's also cheap, widely available, and fast-acting.

Where bleach falls short or causes damage

• General dirt, mud, and grease: bleach doesn't lift oil or particulate dirt well. You need a detergent or degreaser for that.
• Unsealed natural stone: the risk of staining and mineral damage is high enough that bleach is rarely worth it.
• Pet stains and odors: bleach kills bacteria but doesn't fully break down the urine compounds that cause lingering smell.
• Rust stains: bleach can actually make rust stains darker. Use an oxalic-acid-based rust remover instead.
• Anywhere runoff reaches planted beds, ponds, or grass that you care about: chlorine is toxic to plants in anything but heavily diluted amounts.

Step-by-step: how to apply sodium hypochlorite to a patio

1. Gear up first. Put on chemical-resistant gloves, eye protection, and old clothes you don't mind bleaching. If you're working in an enclosed or sheltered area, wear a mask too.
2. Pre-wet the patio. Rinse the surface with a garden hose before you apply bleach. This stops the solution soaking in too fast on porous surfaces and protects nearby plants by diluting any splashback.
3. Mix your solution. For concrete or sealed brick, add 1 cup (about 80ml) of 5%–6% bleach to 1 gallon (4.5 litres) of clean water. For more delicate surfaces, halve that. Mix in a plastic watering can or pump sprayer, never a metal container.
4. Apply evenly. Pour or spray the solution across the surface, working in manageable sections of about 2–3 square metres at a time. Don't let it pool.
5. Dwell time. Let the solution sit for 6–10 minutes. For stubborn mold or heavy algae, you can push to 10 minutes, but don't walk away and forget about it. Work in sections so you can keep moving.
6. Scrub if needed. For thick biological growth, scrub with a stiff-bristle brush while the solution is still wet. On smoother surfaces like porcelain, a softer brush is fine.
7. Rinse thoroughly. Rinse the treated area and all surrounding surfaces, including any plants or lawn nearby, with plenty of clean water from a garden hose. Don't just rinse the patio tiles; flush the edges and any drainage channels too.
8. Repeat for badly affected areas. If growth is still visible after drying, a second application is usually more effective than a much stronger first application.

Keeping people, pets, and plants safe

Personal protection

Always wear gloves and eye protection. Even diluted bleach is irritating to skin over extended contact and genuinely dangerous to eyes. Work upwind if you can, and if you're using a pressure washer to rinse, be aware that spray carries bleach droplets further than you'd expect. Take your shoes off before going back indoors to avoid tracking solution through the house.

Never mix bleach with these

• Ammonia-based cleaners: the combination produces toxic chloramine gases.
• Acids (including vinegar, citric acid, or acid-based patio cleaners): mixing bleach with acids releases chlorine gas, which is genuinely dangerous.
• Other household cleaners: unless the label specifically says it's safe to mix, don't risk it.

Protecting plants, lawns, and ponds

Pre-wetting plants and grass around the patio before you start gives some protection, and rinsing them again after you're done helps a lot. For anything you're particularly worried about (a prized border, a garden pond, a vegetable bed right next to the patio), physically cover it with plastic sheeting before you apply bleach. Chlorine from runoff is toxic to aquatic life, so blank" rel="noopener noreferrer">never let bleach solution drain directly into a water feature or natural waterway. If you're wondering does chlorine clean patios, the key is using the right diluted bleach strength and keeping runoff away from plants and water Chlorine from runoff.

Grout, metal, and other vulnerable spots

Prolonged contact with bleach can lighten or degrade grout, especially older or unsealed grout. Apply carefully and rinse quickly. Metal furniture legs, fixings, or drain grilles can corrode with repeated bleach exposure, so rinse those areas especially well. If you have galvanised metal drains or aluminium edging, consider protecting them with petroleum jelly before you start.

Kids and pets

Keep children and pets off the patio until it's fully rinsed and dry. Even at working dilutions, bleach residue on paws or hands that then ends up in a mouth is a problem you don't want. Once it's properly rinsed and dry, the surface is safe.

Alternatives worth knowing about

Oxygen bleach (sodium percarbonate)

Oxygen bleach is my go-to recommendation for sandstone, slate, and any natural stone where sodium hypochlorite is too risky. If you want a simple answer, the best detergent to clean a patio is the one that matches your surface and target growth, like sodium hypochlorite for algae on concrete or oxygen bleach for natural stone my go-to recommendation. Products like sodium percarbonate release hydrogen peroxide when dissolved in water, which lifts organic staining without the harshness of chlorine. It's safer around plants, gentler on surfaces, and still genuinely effective on algae and mildew. It takes longer to work (20–30 minutes dwell time versus 6–10 for bleach) but the trade-off is worth it on delicate surfaces.

Specialist patio cleaners and algae removers

There are purpose-built patio cleaners and biological growth removers that are worth considering, especially if you're dealing with a specific problem like thick moss or persistent black spot. Many of these use quaternary ammonium compounds or benzalkonium chloride as active ingredients, which are effective biocides without the bleaching side effects. Some also contain surfactants to help with general grime in the same application, which bleach alone doesn't do well. If you're also weighing up detergent-based or multi-purpose patio cleaners, the approach differs quite a bit from using sodium hypochlorite.

Pressure washing

Pressure washing without chemicals removes surface dirt and a lot of biological growth through mechanical force alone, which avoids the chemical risks entirely. For regular maintenance cleaning, a good pressure wash every season often negates the need for bleach. If you're combining pressure washing with sodium hypochlorite, apply the bleach solution first, let it dwell, then use a lower pressure setting (around 1500–2000 PSI for concrete, lower for stone) to rinse and lift the loosened growth. Avoid high pressure on sandstone or slate, as it can erode the surface.

Ready-to-use products vs. DIY dilution

Ready-to-use patio spray products based on sodium hypochlorite are convenient and typically pre-diluted to safe working strengths, which removes the guesswork around concentration. The trade-off is cost: mixing your own from household bleach concentrate is significantly cheaper, especially for large patios. If you have a small patio or want simplicity, RTU products are fine. If you're covering a large area or doing this regularly, diluting yourself from a 5%–6% bleach bottle is more economical and gives you more control over concentration.