Concrete is a relatively low-maintenance outdoor surface, as a concrete patio is often easier to clean and maintain than a wooden deck. However, despite its tough exterior, concrete is porous and easily absorbs liquids, which can lead to tough stains. The texture of the surface also provides plenty of crevices for dirt, moss, and other materials to accumulate.

To clean a stained concrete patio, you'll need something that will also sink in and lift the offending spot. Kitty litter, sawdust and other absorbent materials remove fresh surface spills, but do very little to absorb what sinks below the surface.

Muriatic acid is sometimes used to clean concrete and masonry. But the binder in concrete, Portland cement, dissolves when it comes into contact with an acid. This chemical reaction forms water-soluble calcium compounds, which are then leached away. Plus, acid-based cleaners pull calcium hydroxide out of the hardened concrete, which then quickly forms a white, dusty material called efflorescence. This is a chemical reaction that is hard to control, and the material can become so thick that you'll need to sweep it off of your patio.

Another widely used concrete cleaner is trisodium phosphate (TSP). It is alkaline, so it will not harm your concrete, but it is alkaline enough to cause skin irritation and even burns. TSP is also very bad for the environment. If it ends up in lakes and streams, the phosphates trigger an overgrowth of algae that results in a depletion of oxygen levels in the water, which can endanger fish and other aquatic life.

You can use Simple Green Oxy Solve Concrete and Driveway Cleaner to clean a concrete patio with or without a pressure washer. It removes oil, grease, grime and most stains and discolorations. Its biodegradable formula is safe for lawns and pets. The non-corrosive and non-degrading formula utilizes the natural power of peroxide to provide high-performance cleaning and stain removal without toxic or abrasive chemicals. It is also an EPA Safer Choice Direct Release formula that has been reviewed by toxicologists and deemed safe for environmental contact.

Directions for Cleaning a Concrete Patio

1. Add Simple Green Oxy Solve Concrete and Driveway Cleaner. Pour Simple Green Oxy Solve straight into your pressure washer detergent tank, or drop your siphon tube into the bottle.
2. Rinse with water. Switch equipment to plain water at low pressure and wet the surface.
3. Apply Simple Green. At low-pressure setting, apply Simple Green Oxy Solve to an area that is small enough to be rinsed before it dries.
4. Let sit. Allow the cleaner to dwell on the surface for 3-5 minutes.
5. Rinse with water. Rinse at high pressure, keeping the nozzle at least 2 feet from the surface and the spray perpendicular to the surface.
6. Repeat. Move to a new section and repeat.

1. Make Simple Green mixture. Mix 1 measure of Simple Green Oxy Solve with 20 measures of water in a bucket (example: 1.5 cups Simple Green to 2 gallons water).
2. Scrub. Clean in sections with a soft-bristle brush, paying extra attention to stained areas. Do not allow the cleaner to dry on the surface before rinsing. Do not scrub with a wire brush, as metal pieces can sink into the pores in concrete and eventually form rust stains.
3. Rinse. Rinse with a garden hose at the highest pressure.
4. Repeat. Move to a new section and repeat.

TIP: Clean your patio on an overcast day. Your cleaning solution will evaporate more slowly when the sun isn't beating down on it. It's also a good idea to start cleaning early in the day before the sun has the chance to warm the surface.

TIP: Once your patio is clean, protect it from future stains by sealing it with a concrete sealer. Follow directions on the sealer label.