Can You Paint Over Green Algae?

Can you paint on top of algae?

There are few things as disheartening as seeing green algae and mold growing in the grooves and crevices of your timber decking, fences, or outdoor sheds.

It can be quite tempting to simply rub a bit and paint over the algae so that it is no longer seen.

But is it a good idea?

While it may seem at first that painting over the algae will deny it the oxygen needed to grow. The truth is that the spores will continue to live.

This means that simply painting over them is only a temporary solution. If you want a long-term solution, you must find a way to remove the algae altogether.

Just keep in mind that scraping off the old paint and algae will not always be the complete solution.

In fact, the green algae may penetrate the surface to the point where it hides deep enough not to be removed by scraping alone.

You will need to use a cleaner or treatment designed to destroy the algae, moss, mildew, and mold.

And once you use the cleaner, you may find that you do not have to repaint the surface at all if the inner layer is still in good condition.

Will Paint Cover Algae Growth?

Many brands of outdoor paint indeed have formulations that either slow the growth of algae or prevent it from growing at all.

However, it does not destroy the algae or mold. This means that eventually, it will come through the new paint.

The only advantage of simply painting over the algae is that it will, for a time, cover the green stains.

But within a matter of weeks or perhaps a few months, the familiar green stain of algae will return. So, all that effort you put into a solution does not last.

How Do You Get Green Algae Off Painted Walls?

Removing green algae from old painted walls is important if you plan to repaint them for a fresh look.

Here are a few simple steps that can help you remove algae buildup on walls…

Step 1- Spray Cleaning Solution:

Let it sit for about 10 to 15 minutes, according to the instructions. You will need to start the next step before the solution dries.

Step 2- Scrub:

Use a good stiff brush and scrub the surface. This will remove the algae or mold.

Step 3- Rinse:

When all the algae, mold, or dirt is removed, rinse the exterior walls with a water hose or a pressure washer.

Step 4- Spot Clean:

Inspect the area for any signs of mold or algae that remains. If there are green algae remaining, you can scrub them away using the brush and the cleaning solution.

Finally, let the surface dry naturally.

What Types of Paint Can Be Used to Cover Algae?

If you have an area that is prone to algae growth, such as a deck or patio that is slow to dry, then you should invest in paint that actively resists algae.

Decks or walls that are in shaded areas and receive little sunlight are suitable for algae-resistant paint.

You can use paints such as Cabot DeckCorrect, which resist not only algae and mold but also dirt.

Plus, the paint will fill the cracks in the deck and is skid-resistant so that it stays clean and in like-new condition for a long time.

When you consider that paint does grow more porous as time passes, a new coat will help prevent moisture from forming on the surface.

This will keep any new algae or mold from gathering on the paint and creating more green slime.

In addition to paint, you can find many sealants, oils, and primers that also have properties that resist algae growth.

Plus, such products can help bring out the best in the natural color of the wood used for your decking.

painting over green algae on fence

What Can You Use to Remove Green Algae from Wood Before Painting?

While you can use plain water and some elbow grease to remove much of the algae from the surface, it will not be enough to get at the algae which have settled in the cracks and openings.

You will need to use products such as fungicide or simple bleach that destroys the algae on contact.

1- Oxygen Bleach:

You may choose to use a specialized deck cleaning product, but bleach is cheap and quite effective.

In fact, many specialized deck cleaning products use oxygen bleach, or sodium percarbonate, as it is sometimes known, as its main ingredient.

This product can be found in the laundry section of retail stores.


Do not confuse oxygen bleach with chlorine bleach.

Chlorine bleach may cause damage to the timbers of your deck. While some recommend chlorine bleach, oxygen bleach is far less damaging.

Mix 7.5L of warm water with two cups of oxygen bleach. If your deck has grime, add ¼ cup of liquid dishwashing detergent.

Before you apply the solution to the entire deck, try it on a section that is not seen first to test out its effectiveness.

Keep in mind that some bleach solutions may alter the color of the natural timber.

If you plan to paint over it, go ahead and clean the deck. A paste of oxygen bleach mixed with water should do the trick for stains.

However, since the oxygen bleach may discolor (or even damage the deck itself), there are other products on the market you can use to clean away the algae.

2- White Vinegar:

This simple, cheap product can also be used to kill algae. Use a mixture of white vinegar and water and spray it over the deck.

Then rinse away using clean water from a water hose or pressure washer.

Now, apply pure white vinegar to the surface and use a brush to scrub away the algae. Once completed, you can now rinse off the deck using plain water.

White vinegar is quite effective, but it also requires considerably more scrubbing compared to oxygen bleach.

3- Fungicide:

A commercial fungicide spray may be the most environmentally safe solution. It will kill algae or mold without damaging the grass or plants.

Plus, when you do not rinse away the fungicide, it will continue to kill any new algae or mold that might settle on the deck.

You can use popular brands of commercial fungicides to do the job.

When spraying on the fungicide, you must leave it on for the designated time before repainting the deck or surface.

For green algae, it will generally mean a few days. However, if you have black mold, you may need to leave it on for around a month.

Once the algae have disappeared, you can start the painting process. You should clean the surface again to be sure before applying a new coat of paint.

Related FAQs

Will algae rot wood?

No, algae do not feed on timber. But if algae are present, it means enough moisture exists to cause the wood to start rotting.

Fungi and bacteria also thrive when moisture is present on wood, causing such microorganisms to reproduce. The result is that the wood begins to fall apart.

This is why you should treat the algae as soon as it is seen. Plus, you should take steps to identify and correct surface moisture issues to prevent rot.

Can algae be dangerous?

In an indirect sense, algae are certainly dangerous to wood and wooden garden furniture.

This is because the growth of algae is fueled by moisture building on the surface.

It is the moisture itself that represents the danger to the wood as it causes rot and structural damage.

If you see algae, it’s a warning sign that the wood is in danger.

In addition, the growth of algae and mold can make the deck surface slippery to walk on.

And while most algae forms are only a minor nuisance to humans, the spores from more dangerous forms can be problematic in terms of your health.

Where can I find algae in my house?

You will most often see algae forming on the north side of the home in the northern hemisphere.

This is because the sun does not directly shine on the north side, meaning its ultraviolet rays, which destroy algae and mold, are not directly applied.

The darker the conditions, the more likely algae, and mold will form on your porch and home’s walls, siding, or timber.

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