How to Clean Concrete

A concrete sidewalk is being cleaned by a power washer.

For something that is used so often in our everyday lives, the concrete we walk on is so seldomly noticed or given the attention it deserves. It sits there day after day making our lives nicer and easier and we have the audacity to neglect it. Damn us. We park our dirty, oily, nasty cars on it. We spread salt over it. We even have our little parties on it and allow our grills to drip hot grease all over it. And do we ever even say “thank you” to our concrete? Of course not. Because that’s the kind of people we are. Well, I say it’s time for a change.

That’s right. But don’t be too hard on yourself. You’re not actually a bad person. The thing is, concrete gets dirty so gradually that it’s durn near impossible to even notice what’s going on. Usually, though, after you’ve put the effort into concrete cleaning, you will see the difference you’ve made, and it’ll be abundantly obvious just how dirty it was. Concrete is nothing more than water, aggregate (varying grades of rock, sand, and gravel), and Portland cement, which in the most basic of terms is what binds it all together. That being said, concrete is obviously porous, and those little pores like to collect dirt and grime, which is the main reason why concrete gets dingy lookin’. So, how do you give your concrete the love and respect it deserves? The answer (and the method) is simple. You clean it, and you do it safely and naturally.

Natural Concrete Cleaning

  1. broom and dustpilePrepare for concrete cleaning. The first thing you will want to do is to remove everything that might be in your way. Move cars, furniture, grills, any decorations, plants, etc. Once clear, grab a push broom and sweep the concrete. This will get any big chunks and help you avoid spraying things like nails and glass into the yard or street. Next, put a tarp over any delicate plants and anything else that might get damaged from spray. Finally, cover any electrical cords and outlets. Water + electricity = death.
  2. cleaning solution sprayerMake your own simple concrete cleaner. In a 5-gallon bucket, mix (according to package instructions) some good ol’ oxygen bleach with some hot water. Once the solution is ready, pour it into a tank sprayer and get to work. Spray the heck out of your entire slab of concrete. Go over each section thoroughly and spray enough on so it won’t dry right away. Once everything is properly coated, sit back and wait for about twenty minutes to let the oxygen bleach do its thing.
  3. utility broomTime for some scrubbing action. By far the best way to do this is either with a long handled brush or a push broom. The more you scrub, the better. Make sure, if you’re in the garage, to get the corners really well. Debris and grime have a tendency to build up there. Give every last bit of concrete your utmost attention and take your time doing it. If you don’t clean evenly, the concrete may look patchy when you’re done.
  4. power washing concreteIf you don’t already have one, borrow or rent a pressure washer. This will make a world of difference. To clean concrete, you want a pressure washer that throws at least 4 gallons per minute at 3000psi. This amount of force will be more than adequate. Adjust the nozzle to a fan rather than a stream, and sweep the spray back and forth slowly over the entire surface. Keep the end of the nozzle one to two feet away from the concrete. Again, make sure you clean evenly so you don’t end up with varying levels of cleanliness. All you need in your pressure washer is hot water.
  5. arm and hammer multi cat litterSpot-cleaning concrete. If a complete cleaning is not necessary, there are a couple good ways to clean concrete stains. If the spill is fresh, dump a pile of kitty litter (which you can get from Amazon)over the mess and allow it to sit overnight and soak up the offending goo. If it’s an automotive spill, contact your solid waste department for proper disposal methods. If the concrete stain has been there for awhile, fill a bucket with hot water and mix in the proper amount of oxygen bleach, grab a scrub brush, and go to town. Depending on the stain, you might need to do this more than once. A solution of hot water and laundry detergent works well, too. Never use a brush with steel bristles. Chunks of the brush can break off and cause rust stains.
  6. sealant brushYou’re done for the day, so grab a beer. The only thing left to do now is watch it dry. To speed things up a bit, use a push squeegee to get as much of the water off as possible. If you plan to apply a concrete sealant, you will probably want to wait a couple of days to make sure it’s properly dried before slathering it on. Concrete sealant is a good idea. It helps to protect your concrete from water erosion and the harm caused by cycles of freezing and thawing. At the upper right corner of this page, you will find some suggestions for environmentally friendly concrete sealants.

Dangers of Conventional Concrete Cleaners

We have learned over the years that just because that’s the way Grandpa did it doesn’t mean it’s right. Or, for that matter, safe. Wander into Gramp’s garage, check out his shelves, and you’ll be sure to find containers of TSP (trisodium phosphate), bottles of chlorine bleach, and more than likely a bottle or two of muriatic acid. These are the things he used to clean cement. It’s a wonder the old guy made it as long as he did.

  • TSP, as we all don’t know but sure as hell should, is a very strong base that, if you come into direct contact with, can cause fun things like skin burns, blisters, coughing, sore throat, and red burning eyes. I don’t even want to mention what can happen if you accidentally ingest it. It’s also tough on the environment. The addition of phosphates from TSP in water can cause monster algae blooms that suck all the oxygen out of the water and kill fish. It also blocks sunlight and can be damaging to aquatic vegetation.
  • Chlorine bleach, aside from being a known cause of ozone depletion, irritates mucous membranes, can cause eye and skin irritation, and is hard on the lungs, especially if you suffer from any form of breathing difficulty.
  • Muriatic acid (a.k.a. hydrochloric acid) is probably the most common chemical for cleaning cement. According to the EPA, it is corrosive to the skin, eyes, and mucous membranes. It can also cause coughing, hoarseness, chest pains, corrosion of the esophagus, vomiting, and diarrhea. Along with all that, hydrochloric acid is a component of acid rain.

Environmentally Friendly Concrete Sealants

bucket of cure and sealCure and Seal by Natural Soy Products is designed to be used with freshly worked concrete to retain the hydration water. It can also be applied to exposed surfaces to repel water. It’s made from soy beans and is safe for concrete or wood.

jug of soy sealSoy Seal is another sealant good for waterproofing concrete and wood. As it is made from soy, it is biodegradable and non-toxic. It is sprayable, cleans easily, and each application lasts for over a year.

earthpaint logoEarthpaint E-Coat Sealer is an environmentally friendly, non-toxic, commercial-grade sealant for concrete floors, masonry, siding, plasters, pavers, and more. It is an acrylic resin with citrus solvent.

About the Author

Eric D. Ronning

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