How to Remove Green Algae from Concrete Patio, Driveway, Sidewalk

As a homeowner, ensuring your outdoor concrete surfaces are in excellent shape isn’t just critical for curb appeal; it’s often a matter of safety. Algae buildup isn’t attractive, and since algae is slick, it can increase household members’ and visitors’ chances of a slip and fall. That’s why many homeowners immediately want to know how to remove algae from concrete if they spot it growing on their patio, driveway, or sidewalk.

There are several ways to remove algae from concrete. Pressure washers can do the trick, as well as applying boiling water. A steam cleaner can kill algae, or you can try an oxygen bleach like OxiClean. Commercial algae removers are also often effective.

However, some other strategies can also work well. If you want to learn more about removing algae from concrete surfaces like patios, driveways, or sidewalks, here’s what you need to know.

What Causes Green Algae on Concrete?

Green algae doesn’t require much to grow in an area. Usually, the biggest factor is moisture, as algae needs a moist environment to thrive.

As a result, if you live in a damp or humid region, you can end up with algae. Similarly, excess moisture can promote algae growth if a patio, driveway, or porch doesn’t drain properly after it rains.

Algae is also more common in shady spots. Direct sunlight usually causes an area to dry out, which isn’t ideal for algae. However, it can form in the open if a location remains moist, such as along the edges of an outdoor pool or concrete pond.

Algae doesn’t require soil since it doesn’t develop deep roots. That is why it can end up across concrete, as the texture of the surface is enough to support the algae.

How to Remove Algae from Concrete

There are several techniques for removing algae from concrete, but all require similar preparation steps. First, you want to remove any debris or dirt on the algae, ensuring any treatment reaches the algae. Usually, sweeping the area is enough.

Removing furnishings, potted plants, or similar items from the concrete surface is also critical. That clears out the area you’re working in and makes it easier to check those surfaces for algae growth that may need addressing.

Next, you need to wear some personal protective equipment. Gloves and goggles are essential, as well as closed-toed shoes. If you’re using a chemical-based approach, a breathing mask is also a wise addition.

In some cases, you may want to wear disposable coveralls. Some chemicals can damage or discolor fabrics. With disposable coveralls, you protect your clothing from splashes or other forms of contact.

Depending on your solution, you may want to cover nearby plants with tarps. That ensures that any splashes don’t contact the plants, protecting them from accidental damage.

You’ll also want a garden hose connected to a nearby water source. Some algae treatments require a rinse after you’re done. A hose lets you dilute any chemical runoff that hits your lawn or nearby plants, reducing the odds of harm.

1. Pressure Washer

Another strategy for removing algae from concrete is a pressure washer . The high-pressure water stream can easily push the algae off your concrete. Plus, you don’t have to use chemicals, though you may have the option of adding a cleaner to a reservoir if you’d like.

Before you begin, you need to prepare the pressure washer. Fill up the water tank to the recommended height. Then, turn the pressure down to a low setting and choose a discrete location on the concrete surface with algae as a test spot.

Keep the pressure washer’s nozzle about 12 inches from the concrete surface. Then, use the pressure washer on the test spot, and if the algae doesn’t come up, slowly increase the pressure a little bit at a time. The goal is to find the lowest pressure setting that does the job, as that reduces your risk of accidentally damaging the concrete.

Also, use a sweeping motion, ensuring the nozzle moves the entire time. Focusing too much on a single spot could make damage more likely, so ongoing movement is critical.

Work a small section at a time, moving the nozzle back and forth until that spot is clean. Then, move on to a different area, and continue the process until the algae is gone.

2. Boiling Water

If you only have a few smaller algae spots, boiling water is potentially all you need. The high temperature kills the algae, allowing you to remove it without chemicals. Another benefit is that this is easy to prepare, as you only need a stovetop and tap water in most cases.

For small spots of algae, consider using a teakettle to prepare the boiling water. The benefit of using a kettle is that it’s designed to hold hot water and has a spout to ease application.

For larger areas, you may want to fill a stockpot instead. While some people recommend using a bucket, some plastics may warp due to the high heat, so keep that in mind if you’re bucket is plastic.

Also, be mindful of splashes during the application. The high water temperature can harm nearby plants and burn people or pets, even if it’s just a splash.

After saturating the algae in boiling water, you’ll need to scrub it to remove it from the surface. You’ll want to use a nylon brush or stiff-bristled broom, as those won’t harm your concrete.

Once you’re finished scrubbing, use a garden hose to rinse the debris away. Just be aware that boiling water won’t necessarily address any stains left by the algae, so you may need to apply baking soda or a stain-removing cleaner or solution to address any discoloration.

3. Vinegar

Vinegar is highly acidic, so it can work as an algae remover. However, the high acidity also means it can damage your concrete, particularly if it’s not properly diluted. Plus, vinegar can damage other plants and grass.

If you try this approach, choose a hot, sunny day. High temperatures and direct sunlight make this approach more effective.

Next, put one cup of vinegar in a spray bottle. Then, fill the rest of the bottle with water. Spritz the algae carefully, ensuring you limit any splashes.

If any vinegar gets on a nearby plant, take your garden hose and rinse it immediately. The rinse reduces the chance that the vinegar will harm those plants, as the contact time is minimized.

Let the vinegar solution sit on the algae for a bit. After that, you’ll need to take a nylon brush or stiff-bristled broom and scrub the algae away. Once the algae isn’t stuck to the concrete, use a garden hose and rinse the entire area thoroughly to remove the vinegar residue and dilute any runoff.

4. Bleach

Bleach can kill green algae on concrete, but it’s not the safest choice. Bleach is a dangerous chemical that can harm people, pets, and nearby plants. Plus, it can damage any paint or coatings on your concrete.

Generally, you should only use bleach on untreated and unpainted concrete surfaces. You’ll also want to do a test spot in an inconspicuous area to ensure the bleach doesn’t cause discoloration or other damage. Additionally, have a garden hose nearby to quickly rinse any plants splashed accidentally during application.

Before you begin, dilute the bleach. Usually, one cup of bleach to one gallon of water does the trick. Pour the solution into a spray bottle to make the application simpler. Then, thoroughly spritz the algae and let it sit for about 15 minutes.

After that, you can take a nylon brush or stiff-bristled broom to scrub the algae away. If stains remain, you can apply more bleach solution, let it sit again, and scrub once more to try and remove them. Once that’s done, rinse the area thoroughly with a garden hose.

5. Steam Cleaner

Using a steam cleaner lets you kill the algae with high heat. It’s a chemical-free option, and it won’t harm nearby plants if you keep the nozzle away from them while you work.

You’ll want to review any instructions that come with your steam cleaner before you begin. However, most operate similarly. Fill the water tank, let the machine warm up, and then you’re ready to get to work.

Steam the algae by moving over it slowly with the steam cleaner. Be mindful of the position of the nozzle, as the high heat from the steam can burn people, pets, and other nearby plants.

After you steam all the algae, you’ll need to scrub it to remove it from the concrete. Use a nylon brush or stiff-bristled broom to get it up. Then, rinse the area with a garden hose to remove any remaining debris.

A steam cleaner may not address stains left by algae. As a result, you might need to follow up with a stain remover if any discoloration remains.

6. OxiClean

OxiClean is an oxygen bleach that won’t harm clothing or damage your concrete. Along with killing algae, it’s also an effective stain remover, so you can use it to address discoloration that may remain once the algae is gone.

You have a few application methods available. You can take half a scoop of OxiClean and add it to a spray bottle. Then, fill the bottle with water, stir or shake it to combine, and spray the algae.

Alternatively, you can add four scoops of OxiClean to a gallon of water in a bucket. Stir it thoroughly to combine. After that, use a sponge or mop to apply the solution to the algae.

Once the OxiClean is applied, scrub the surface using a stiff-bristled broom or nylon brush. Let the solution sit for about 30 minutes, then scrub again. Finally, use a garden hose to thoroughly rinse the surface.

If stains or discoloration remain, apply more OxiClean solution to them. Scrub the spot a little, let it sit for 30 minutes, then rinse again to see if the stain is gone.

7. Commercial Algae Remover

Another option worth exploring is commercial algae removers. These products are designed to handle algae and usually deliver good results. But they may involve chemicals, so caution during use is often necessary.

If you go with a commercial algae remover, how it works and the required application method may vary. Each product is different, so you want to check the manufacturer’s directions to ensure safe use and to get the best results.

Wet & Forget Moss, Mold, Mildew & Algae Stain Remover is a solid choice if you prefer a commercial cleaner. All you need to do is mix one-part stain remover with five parts water in a garden sprayer and apply the solution to the algae as directed by the manufacturer.

Ideally, you want to use the stain remover on a cool day – but above freezing – without any rain in the forecast, as it needs to soak for several hours. Additionally, it works over time, so you won’t see results immediately.

However, no rinsing or scrubbing is required, making this commercial algae remover a relatively low-effort approach. It can also work on multiple surface types and handles more than algae, so it’s a versatile product.

Does Salt Kill Algae on Concrete?

High concentrations of salt can harm some types of algae. Usually, you want to make highly concentrated salt water and apply it with a spray bottle. The issue is that salt water can also harm nearby plants and your lawn, so this isn’t necessarily the ideal approach.

Additionally, using salt alone isn’t ideal compared to the options above. That’s especially true since some types of algae are highly salt tolerant, so simply soaking it down with saltwater may not kill the algae.

Still, you can use salt to increase the scrubbing power of another solution. For example, sprinkling the algae with salt before applying vinegar and scrubbing could make removal easier. Salt is coarse but not to the point that it would damage the concrete, so it could help get the algae up without harming the surface.

Does Baking Soda Kill Algae on Concrete?

Baking soda is an option worth considering, especially if you have a string of warm, dry days in the forecast. Mix 2 to 3 tablespoons of baking soda in a spray bottle filled with water. Then, spray down the algae thoroughly and let it sit.

After a few days, the algae should dry out, making it easier to remove. Then, you can use a stiff-bristled broom, scrub brush, or pressure washer to get rid of the algae.

Just make sure that you apply the baking soda solution with care. It can potentially harm nearby plants or your lawn. If you accidentally get the cleaner on your grass or a plant, rinse that spot with water to reduce the chances of damage.

What Is the Best Concrete Sealer to Prevent Algae?

Generally, the best concrete sealer to prevent algae is labeled algae-resistant. Along with being protective, penetrating surface protectors, they often contain inhibitors that slow or stop the growth of algae. They may also protect against mold and mildew, which is handy if you live in a damp climate.

Typically, applying the sealer is relatively straightforward. First, you’ll need to clean your concrete surface and make sure that any algae, mold, or mildew growth is addressed. While application methods can vary, many can be applied using a sprayer to ensure you get an even coat.

After application, the sealer is usually dry to the touch relatively quickly. However, you’ll need to let the surface fully cure before use. You also want to remember that some sealers require more than one coat, so review the directions to see when you need to apply it.

Additionally, sealers are often long-lasting, but they won’t hold up indefinitely. Review the manufacturer’s product information for lifespans and watch for signs of damage over time. If the sealer starts wearing away, it won’t be effective, so reapply if you notice wear.

Best Way to Get Rid of Algae on Concrete

Any of the options above can work well if you need to remove algae on concrete. If you want to avoid chemicals, boiling water, steam cleaning, or pressure washing are good places to start. OxiClean is effective and low-risk, and you can try commercial algae removers if you’re okay with chemical approaches. If you try bleach or vinegar – which can work – just be mindful of the risks.

Did you learn everything you wanted to learn about removing algae from concrete? If so, let us know in the comments. Also, if you know someone fighting with algae on their concrete patio, driveway, or sidewalk, share the article.