How do I Remove Green Algae from my Patio?

Green algae are types of seaweeds that grow in damp areas. In your home, you will found them growing on patios, concrete basement floors, walkways and stone walls. Algae is deep green in appearance and slippery to touch. The sea weed lack true stem, roots or leaves but can spread so fast if not treated.

Homes located in constantly humid areas battle concrete greening caused by algae and moss.

Although the plant may not cause structural damage to your surfaces, algae can permanently stain or discolor the affected areas.

Further, algae is a safety hazard especially when they grow on walkways due to their slippery nature.

There are various ways of getting rid of green algae and mold on a concrete patio. Removing algae and other fungus such as molds prevent your patio from turning green and making it a safe place for your family members and pets. By doing so, you also avoid costs of repainting or acid staining your outdoor hard surfaces.

How to Remove Green Algae from Patio (Bricks, Concrete)

To get rid of algae and fungus, you will need the following:

  • Hand gloves
  • Dust mask
  • Hot water
  • Stiff deck broom
  • Vinegar or bleach
  • Pressure washer


1. Self-Preparation

Put on your rubber gloves, protective shoes, clothing and dust mask before you begin your task. Mold and algae spores are very dangerous when inhaled. Cleaning methods and chemicals used for removing algae such as steaming and chemicals might also be harmful to your skin.

Clear the affected area by removing any objects and large debris before you begin. Seal off any ventilation if you are dealing with large indoor areas to prevent the toxic spores from being airborne. And remember to wash your clothes immediately you end the mission.

2. Drying out the affected surface

It is safe and easier to remove algae when the area is dry. Algae spores thrive and spread in the air when the environment is moist. Removing them in such conditions can make you inhale such pores and that will be dangerous to your health.

To limit the movement of pores, allow sunlight to strike and dry out the area. If there is no sunlight, use fan or heater.

When the surface is completely dry, take a stiff push brush or deck broom to sweep and scrub the affected area on your patio. You may use a plastic scraper if the weeds are stubborn.

3. Pour hot water

Pouring hot water not only kill the algae tissue but also soften them before they are washed away. Be careful not to splash hot water on nearby grass or important plants.

Drying out and sweeping the surface automatically gets rid of small amount of algae. For large amounts the next step applies.

4. Pressure washing

To completely remove green algae from your paving stones, walkways and driveways, you need to hire or purchase a pressure washer. It can either be cold water or hot water model that is commonly known as power washer. I personally prefer a hot water pressure washer since it sanitizes and remove molds, grime and algae from my patio very fast and easily.

When using a pressure washer, be sure to test on a small area before using on your entire area to see if the surface can withstand the water blast. The powerful water jet from a pressure washer machine can damage a concrete patio especially when directed at one place for a long time. Always move it back and forth during the cleaning.

A power washer cleaner is also the best choice for cleaning your patio or concrete. The hot water is good for killing any microorganisms such as bacteria and fungus found on your surfaces. It acts as a steam cleaner that is commonly used for sanitizing or disinfecting surfaces in many homes.

To start your cleaning, fill your steamer with water and allow it to warm up so that steam is produced. Move the machine over the area as it blast steam on the green algae. After steaming, scrub the area with a deck brush and finalize with a rinse of clean water.

5. Use Vinegar or Bleach

Vinegar and bleach are popular cleaners in many American households which can also be used to will kill algae and mold on concrete.

When using bleach to kill fungus growths and clean your hardscapes, you should be concerned about plants or grass bordering these areas. Bleach can have detrimental environmental effects to plants and environment at large.

You can also read our in-depth guide here on the best detergents and soaps to use in your pressure washer!

How to use bleach

Before using bleach, test on a small hidden area to avoid the risk of discoloring your surfaces. To use this ingredient, mix 1 cup of bleach and 1 gallon of water in a bucket. Scrub the mixture into algae and allow 15 minutes for the seaweed to die before rinsing with a clean hose.

Just like bleach, be careful when using full-strength vinegar to kill green algae on your concrete or brick pavers. Vinegar kills weed and most plants including lawn grasses. Ensure that you are not over-spraying or allowing it to flow to into your flower bed.

How to Use Vinegar

Mix vinegar and water in the bucket and spray the mixture on the algae stained area. Give it 10-15 minutes to kill all the weeds and scrub using a stiff brush in a forth and back motion. Rinse everything with a clean water hose. If there is minimal change, repeat the process.

6. Commercial cleaners

Overgrown algae may be stubborn to remove using any of the above mentioned methods. If any fails to work, find a suitable patio algae cleaner. They are formulated with special ingredients that will eliminate any stubborn algae on your outdoor surfaces.

The product I have had the most success with in recent years is Wet & Forget. It’s fairly inexpensive and I used it on a patio a few months ago that was absolutely covered in moss. Within a week it was gone and I have not seen any moss reappear. One other thing I love about the product is that it is bleach-free. Bleach is a great stain remover but if I can find an alternative product that is nearly as good and does not kill my plants, I’ll take the alternative any day.

Mold or algae stain removers may also be used when you are dealing with a tough stains left behind after removal of the algae. To use your cleaner or stain remover, spray the formula or the stain or affected area and allow 15 minutes before scrubbing and finally hose with clean water.

Before using any product, test on inconspicuous area. Read instructions and use as directed. Some products contain ingredients that may be harsh on your bricks or concrete.

7. Rotary Head Cleaner

A rotary cleaning head is much better for cleaning patio slabs and other outdoor surfaces. Other than making your cleaning effortless, it ensures green algae, mold and other stains are gone for good.

This machine has a strategically angled water jet that provides maximum cleaning impact without much threat to any jointing of the paving itself. Further, the protective hood of the machine prevents any dislodged debris from being scattered onto adjacent surfaces.

After removing algae from the pavers, some of the joint sand may also have been washed away. You can replace the sand by simply pouring joint sand over the pavers and sweep it into and across the joints using your stiff brush. Sweep any that is in excess and store it for future use.


Since algae and molds are formed as a result of damp or moist environment, you can prevent them by drying out your surfaces, covering or screening your patios to prevent rain and ensuring a proper ventilation in closed areas of your home. Prune bushes and overhanging trees around, drain out pooling water and move patio furniture regularly.

Leave a Comment