Home Cleaning Tips How to Clean Concrete Pavers and Patios for Mold

How to Clean Concrete Pavers and Patios for Mold

by Catherine

Has it been constant dreary weather and rain where you live? Our days are wet ones here. As soon as Daylight Savings hit and the days got shorter, it has rained without ceasing in Tennessee. Not good for the mood, but my outdoor plants certainly love it.

Speaking of plants and things that love moisture, can we talk about a common outdoor mold/fungus problem? Most of what I write about here on the blog focuses on indoor mold and your health and wellness, but today I am going to shift gears a little. I am going to write my response to a reader’s question on Tim Carter’s Q & A column in The Washington Post, called “Ask the Builder.”

As you can see from the column’s name, a reader writes in with a construction, home repair, or building dilemma and Tim writes back with an answer from his professional builder’s perspective. This time, the reader’s question concerns a common outdoor mold problem—one that we have also battled at our home: mold growth on a paved patio.

Here is the reader’s question and an excerpt from Tim’s response as written in the column: (Note: If you are interested in reading the whole correspondence, you can do so HERE.)

Dear Tim: My wife and I have an outdoor patio with colored precast concrete paving blocks. It doesn’t take long each year for black mold and mildew to start growing 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.

Loren: I used to have the same problem on two massive 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.

Let’s talk about why the moss, mold and mildew grow in the first place. Moss, mold and mildew need food to survive, just like you and I. The food sources are assorted, just as humans’ diets are. Dusts, 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.

Water is the only other missing ingredient needed to fuel the moss, mold and mildew. 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.

Let’s discuss power washing. There’s a raging debate in the home improvement community about whether power washing can be destructive to concrete, brick, precast pavers and wood. The unequivocal answer is yes — it’s destructive.

The rate of destructive force is directly proportional to the pounds-per-square-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 flowing over rock can do damage.

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 had copper plates on their hulls so barnacles and other marine life would not grow on the wood below the water line.

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

The easiest way to apply the copper is to buy copper sulfate crystals. This is available online, and the blue crystals dissolve readily in warm or hot tap water. 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 are plenty to treat the average-size patio.

I’d apply the solution when the patio is dry as a bone. Apply just enough so the pavers get nice and wet but not so much that the solution runs off into surrounding vegetation. You don’t want to poison expensive landscaping nearby.

You are going to have to reapply the copper solution because normal rain water will leach the copper back out of the pavers. –Tim

Ok. Seems like a pretty well-thought out answer, right? Kind of, but, in short, here are my problems with it:

(1) Tim never addresses the possible constant sources of moisture to the pavers (I’m not just talking about rainfall here) that causes them to never fully dry out and to have a reoccurring mold problem; (2) He doesn’t address the fact that power washing, regardless of the fact that it is destructive to the pavers, provides more moisture to the mold and therefore aids in its growth; (3) He advises the homeowner to use a potentially toxic substance to clean an area where people, pets and vegetation are and can be harmed by getting it on their skin, eating it, or absorbing it.

I know I may sound a little over-the-top, but this sort of thing really gets to me–trusted professionals, like doctors, mold remediators, and builders giving advice that ONLY addresses the symptom, but neglects the underlying issue, and, by doing so, creating further problems or worse dangers. Now, I obviously realize that Tim is giving the best and soundest advice he knows, and I also realize that I am NOT a professional builder. Tim is strictly trying to get rid of the mold. He is not trying to improve the overall situation or the health of the home.

What I do know, is mold, though. I have spent years learning about natural, non-toxic products that can be used to clean and eliminate it without harming me or my family. Thus, I feel pretty well-versed in being able to answer this specific question. I also have spent lots of my time learning about mold prevention in indoor environments, so I feel like I can address that “unanswered” part of the question as well. I know, you didn’t even see that part, but, trust me, it is there.

So, in an attempt to give my “mold- and health-centered” perspective on this topic, I am also going to respond to Loren’s question with my unsolicited advice.

Here it goes:

Dear Loren: I am sorry you are having this trouble with the pavers on your patio. Tim definitely got the basics on mold growth correct with the water and food source pieces, but what he neglected to mention is the fact that you might want to and need to address the whys behind the reoccurring mold and algae in this particular area outside of your home.

The first thing to look at is your backyard drainage system. From what I can tell from your question, this patio sits right off of your home, correct? If that is the case, that means that when it rains or you water your backyard landscape, water is running towards your home and onto or underneath the pavers. This is not good in terms of possible moisture intrusion to your home or flooding that could occur with lots of rainfall. Water running towards your home is NOT good mold prevention for your patio or for the interior of your home. It will eventually start to come inside, and you DO NOT want that issue.

Whatever the case, you should address drainage. If moisture is constantly flowing towards these pavers, the ground underneath them is most likely constantly wet. Therefore, they will never fully dry out and the mold will continue to come back no matter how or what you clean them with. You can irrigate and install drains in your yard that will easily solve this problem. (French drains are the specific ones that will collect and divert the water.  These are the ones with rocks and drainage pipes  below to collect the water and steer it around the home or toward a drain.) Just watch where and how the water flows at the next rainfall or major landscape watering and you will have your answer as to whether or not this is an issue. We had a drain installed to the right of our patio where the water was running before pooling and sitting under our pavers and the difference in mold and moss growth was astounding. We haven’t had the algae that makes the area so slick in a year!

The other piece of this puzzle is sunlight. Is any sunlight getting to your pavers? Is the area covered by trees or an awning? If foliage and tree cover are the case, you might want to consider doing some landscaping or tree removal that give that area more natural sunlight. The sun’s rays are a powerful mold retardant. Sunshine will help to keep the pavers dry and will prevent future mold growth. If you have a retractable awning, consider pulling it back during the hottest times of the day when the sun is most powerful, so that it can do it’s job on the pavers.

Now for my answer to cleaning the existing mold off of the pavers:

Like Tim, I do NOT recommend power washing. Using water to get rid of mold is counterproductive. The force of the jet might “clean” it off temporarily, but it will ultimately inject moisture into the pavers, feeding the mold and never solving the problem. Without a thorough understanding of the “craft” of using a power washer, you will inevitably cause small divots in the cement. These divots collect the dust, mold and protect the water causing significant growth.

I would also NOT recommend using the copper. If the mere mention of the copper solution running off onto your grass and landscaping and possibly poisoning them sets off alarm bells, do you want to be handing the solution or walking on the area with bare feet or allowing your pets outside onto the pavers that you treated with it? I wouldn’t feel safe having any compound that could potentially harm anything in my home or yard used in an area where I intend to spend time.

In spite of the micro-nutritional value of copper to the human body, too much copper is toxic to humans and animals. Heavy metal poisoning is a terrible illness, requiring chemical binders to detoxify humans.  There is lots of literature on copper toxicity. Copper-based paint has been used as an anti-fouling agent in boats for many years.  However, Washington State it the first state to ban use of copper paints on recreational boats and other states are investigating copper. The EPA is currently investigating copper for its toxicity. Copper Sulfate Crystals are purchased in plumbing departments and are used for tree root control in drain tiles & septic systems.  There are many precautions when using.  The other less aesthetically pleasing side of copper is the fact that it can cause a bluish green stain on whatever it is used on. Not a good look, especially on pavers.

My advice as far as removing the mold, and this is from my personal experience using this method, is to use EC3 Laundry Additive at 1/3 bottle in a one gal spray or put into a garden hose mixer.

Spray the entire area and allow it fully dry. Then, you can use a scrubbing brush and some elbow grease to remove any visible mold. Spray again and allow to air dry. If you have an area with a large concentration of mold or algae, use the laundry additive undiluted with your scrub brush. This will kill what is there and will prevent further growth.

The laundry additive can be walked on with bare feet, you do not need to wear protective gear to apply it, and your pets can lick it without it harming them. The mixed laundry additive will last about 2-3 months.

Good luck! I will reiterate to look into what is causing the moisture to congregate on the pavers first, though, because if you address that, you will not find yourself having to clean them for mold so frequently. You will also do great work in preventing water intrusion to your home and a possible indoor mold problem, which is a LOT more difficult to solve.

Have you ever read an advice column and thought about authoring a correction? I can’t be the only one. Hopefully you folks will let me know if I ever write something that you don’t agree with!


Share this:

You may also like

Leave a Comment