Q&A / 

Patio Moss Mold and Mildew Prevention

patio moss mold

Patio Moss Mold and Mildew Prevention | This ugly black mold and mildew on the patio can be prevented with a simple spray-on solution! (C) Copyright 2017 Tim Carter

"Moss, mold, and mildew need food to survive, just like you and me. The food sources can be an assortment of things..."

Patio Moss Mold and Mildew Prevention Checklist

  • Moss, mold, mildew, and algae feed off invisible food and water
  • Pressure washing can damage precast colored pavers and brick
  • WATCH the copper sulfate video below!
  • Copper sulfate is the secret to STOP moss, mold, algae, and mildew on your patio
  • CLICK HERE to Get Tim's FREE & FUNNY Newsletter!

DEAR TIM: My wife and I have an outdoor patio constructed with colored precast concrete paving blocks. It doesn’t take long each year for black mold and mildew to start to grow on it.

We also have an issue with moss and algae growing on it. I have to power wash it at least once a year and wonder if there’s a way to prevent the moss, mildew, and mold from growing in the first place.

Am I damaging my patio with the power washer? Why is it growing on the precast concrete pavers? This problem can’t be that hard to solve. Loren P., Okatie, SC

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DEAR LOREN: I used to have the same problem on two massive solid-clay brick paver patios in the back of the last house I lived in. It was a mind-numbing job that took hours and hours of work to restore the patio to brand-new condition each spring. I hated doing that job.

Why Does Patio Moss Mold Grow?

Let’s talk about why the moss, mold, and mildew grow in the first place. Many years ago, I couldn’t understand how it could grow on solid rock, precast concrete or brick, but now it’s crystal clear to me as I’ve attained more knowledge.

Moss, mold, and mildew need food to survive, just like you and me. The food sources can be an assortment of things just as we humans have countless different things we eat.

Dust, ultra-fine sugar aerosols from trees and bushes, tree sap, minerals, organic debris, etc. are all food sources for the unsightly things growing on your patio.

Free & Fast Bids

CLICK HERE to get FREE & FAST BIDS from local handymen that can apply a magic solution (see below) to STOP algae, mold and mildew on your patio.

What is a Fast Test to Grow Mold & Mildew?

You can do a fast test that produces dramatic results by just pouring out a small amount of carbonated soda that contains sugar or high-fructose corn syrup on your patio. You might have mildew growing on the spill in as little as forty-eight hours if you do it in a shaded area of your patio.

Water is the only other missing ingredient needed to fuel the moss, mold and mildew since their spores are constantly falling down on your patio. If you could keep your patio completely dry, you’d not have any growth.

But even morning dew is enough to sustain the green and black organisms. They’re tenacious and know how to make a little water go a long way.

Will Power Washing Damage My Patio?

Let’s discuss power washing. There’s a raging debate in the home improvement community about whether or not power washing can be destructive to concrete, brick, precast pavers, wood, etc. The unequivocal answer is yes - it’s destructive.

patio moss, patio mold

©2017 Tim Carter

The rate of destructive force is directly proportional to the pounds-per-squares-inch (psi) power the machine delivers, the angle of the spray-wand tip and the distance the tip is from the surface being cleaned. You just have to look at the Grand Canyon to understand that water simply flowing over rock can do damage.

Water directed at a surface with 1,500 psi or more can do immense damage on softer surfaces and it does cumulative damage to harder surfaces with each successive washing.

Will High Pressure Remove Colored Cement?

In your case power washing will rapidly remove the colored cement paste that covers the small sand and gravel particles in your precast pavers. If you had a saved paver in your garage that the installer left behind that’s never been washed or exposed to the elements you’d notice that it’s got a uniform color over the entire surface.

This uniform color is created by an ultra-fine layer of pigmented Portland cement that coats the sand and small gravel in the pavers.

After one or more washings, you’ll start to notice the individual colors of the different sand and gravel that was used to make the pavers. The colored cement will still be there between the individual particles of sand and gravel.

CLICK HERE to get FREE & FAST BIDS from local handymen that can apply a magic solution (see below) to STOP algae, mold and mildew on your patio.

How Do You Prevent Patio Moss Mold Growth?

The good news is you can prevent the growth of patio moss, mildew and mold. All you have to do is borrow technology developed hundreds of years ago by mariners.

Clipper ships and warships that depended on speed to make money and win wars employed the use of copper plates on the hulls of the ships so barnacles and other marine life would not grow on the wood below the water line.

patio moss mold

Patio moss mold can be prevented using copper sulfate. ©2018 Tim Carter

Is Copper a Natural Biocide?

Copper is a natural biocide. It’s pure, it’s pretty much harmless to mammals and it’s found in multi-vitamins that you might take to stay healthy. Copper in our bodies helps us to retain iron and it aids in producing the energy you need to get through the day.

You can’t cover your patio with copper sheets, but you can spray on a liquid solution of copper that will soak into the top surface of the concrete pavers. This copper will stop the growth of the pesky green and black organisms in their tracks.

Do You Dissolve Copper Sulfate In Water?

The easiest way to apply the copper is to purchase copper sulfate crystals. This is readily available online and the blue crystals dissolve readily in warm or hot tap water.

bowl of copper sulfate

This is copper sulfate. It dissolves easily in water. Spray it on with a hand-pump sprayer. CLICK THE IMAGE TO ORDER THE COPPER SULFATE NOW.

I’d mix 1.75 pounds of copper sulfate in each gallon of water. My guess is you’ll discover that two or three gallons of water is plenty to treat the average-sized patio.

Copper Sulfate Video

Watch this funky video about copper sulfate. This guy is spot on with his advice!

Is it Best to Apply To Dry Pavers, Concrete or Brick?

I’d apply the solution when the patio is dry as a bone. You want the solution to soak into the surface. Concrete is absorbent unless it has a shiny steel-troweled finish.

Most exterior concrete is rough, so the solution will soak in. Apply just enough so the pavers get nice and wet, but not so much as the solution runs off into surrounding vegetation. You don’t want to poison expensive landscaping nearby.

How Often do I Apply The Copper Solution?

You’re going to have to periodically re-apply the copper sulfate solution because normal rainwater will leach the copper back out of the pavers. I can’t tell you how often because it’s a function of the amount of rainfall where you live. But I do know it’s far easier to apply this solution in minutes rather than bend over for hours and hours using a power washer!

CLICK HERE to get FREE & FAST BIDS from local handymen that can apply a magic solution (see above) to STOP algae, mold, and mildew on your patio.

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23 Responses to Patio Moss Mold and Mildew Prevention

  1. Will your Cooper sulfiate solution also work on mold that appears on vinyl siding instead of using "wet and forget" product

    • You can try it. The Wet-and-Forget product is a VERY WEAK solution of copper sulfate. Based on what I've seen, there are quite a few bad reviews of it.

      Go above and CLICK the links I provide to get some pure copper sulfate. FOLLOW my directions in the column to mix. Apply with a hand-pump garden sprayer.

      Your biggest issue is you'll have to apply it more often as rain will wash away the copper. It can't soak into the vinyl as it would SOAK into concrete or other porous material.

    • No. The sidewalk does not have to be cleaned first. The copper will begin to immediately kill the mold, mildew and algae. You may want to apply it twice within one week.

      Wait for when there's no rain in the forecast for at least a few days.

  2. I used the copper sulfate on a small area of pavers and it turned the lighter colored ones green. Will this go away any time soon?

    • You're seeing the oxidized copper. Yes, the color will change. You need to decide if you want green algae on your pavers or if you want nasty slippery green algae, moss, black mold and mildew or have a small amount of green coloration instead.

      It's one or the other.

  3. I am confused by the vid vs the text I read. Once you mix it to saturation, do you dilute it again when you apply to pavers, or stick to the 20%? Also does the blue color go away?

  4. Wow - I am going to use this spray, I have the copper sulfate. I spend hours yesterday pressure washing my brick walk with a strong bleach applied first. Ugh - slow, real mess, and not that effective. Thank you, thank you. Can't wait til it gets below 90 outside and I'll work on it.

  5. I think you should tell your viewers that copper sulfate is used to kill tree roots. The concentration you recommend could wash into the soil and kill everything for years.

  6. You are mixing way too much. Its 3 tablespoons per gallon mixed, use a garden sprayer and wet the pavers, or landscape rock, sinew of your house, etc and wait...let it go a week and reapply if needed. Then perhaps once every 3 to 6 months depending on rain levels.

  7. I am a little confused by your video also. I have several very large clay brick patios and walkways along with Bluestone and lannon stone borders around my house located in a woods. The site is partial sun/shade even though we rutinely remove trees to bring in more sunlight, however we still get mold, mildew, algae etc growing. I would like to use my 3 gallon hudson backpack sprayer and apply your recommended solution of copper sulfate selectively on those areas needing it. How much 20% liquid copper sulfate solution do I add to my 3 gallon water? I have extensive plant material around my patios/walks and do not want long term leaching into soil to kill plantings.... As my profession is a Landscape Architect I will be seeking solutions that I can pass on to many clients as well. Also the green/blue tint of color the previous comments have mentioned will this be a permanent color or only temporary and if so for how long? Thanks for your help in this area.

    • Ed,

      I provide the mix ratio above right under the bowl of copper sulfate crystals. That's NOT my video, but one I found on YouTube that sort of shows what to do.

      Use MY RATIO for the best results. Apply to DRY masonry and do not overspray onto nearby vegetation. MULTIPLE coats same day is preferred so lots of solution soaks into the top 1/4 inch of masonry.

  8. Tim,
    The copper sulfate worked great on my clay brick pavers. Months later, they still look like new. The blue color did not remain long and I even soaked them good! Thanks again.

  9. I put a couple older pennies (60's or older) in a spray bottle of white vinegar and let it sit until it gets a little green color (about a month) then simply spray my cement, wood or siding with this now dilute acetic acid/copper acetate solution and within days the green color vanishes and becomes gray. This washes off easily. Cheap and safe. I would rather do the quicker chemistry thing with copper sulfate but can never seem to find it easily. Very green (literally) and uses what everyone has in their home already.

  10. I have a concrete tile roof in Western Washington state. Not ideal because of moss growth. Will copper sulfate kill and prevent the moss? Is it safe for the roof and plants beneath it? If so, should I stick with the 1.75 pounds per gallon that you recommend for patios?

  11. Please respond to my post above dated sept 26 2018. I have not received a reply yet. Also wondering if applying during the cold winter months providing things a very dry and no snow is better or worse than warmer months. Thanks Ewald

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