How to Clean Concrete Floors

Cleaning outdoor concrete flooring is different from indoor concrete flooring. Here's how to remove dirt and mildew from both surfaces without causing damage.

October 21, 2021

Concrete is a sturdy material for indoor and outdoor floors. It’s durable, easy to clean and somewhat resistant but not impervious to stains. It’s porous and will soak up dirt, spills and harbor mildew. Tough as concrete is, it will need periodic scrubbing. Here’s how to clean concrete, both indoors and out.

White Modern Kitchen

White Modern Kitchen With Copper Pendant Lights

Copper-colored globe pendant lights and a wood picnic-style dining table make for a compelling contrast in this white modern kitchen. The glazed concrete floor adds another layer of interesting texture.

Photo by: Julie Soefer

Julie Soefer

A power washer is the easiest way to clean concrete outdoors. You should be able to blast away dirt, mildew and grime in an afternoon. Rent one and read the instructions on how to use the machine before you start the project. Spray the patio surface with a detergent and use a stiff brush to scrub it into the concrete. Never use a metal-bristle brush. Metallic fibers can get trapped in the porous surface of the concrete and rust. Put on safety goggles and gloves. Turn on the pressure washer. Move the wand from one side, using the same motion as you would if you were mopping a floor.

How to Remove Stains From Concrete

There are several options. You can use bleach, ammonia (Note: never mix the two) and other commercial solutions. For a natural solution to stubborn stains on interior concrete floors, mix flour and hydrogen peroxide into a paste the consistency of peanut butter. Spread it over the stained area. Let sit overnight. Then, scrape with a plastic-edged scraper tool.

Trisodium phosphate (TSP) mixed with water and scrubbed onto the stained area with a nylon bristle brush can remove tough stains. Scrub until the stain is gone and rinse with a hose. TSP is available at home improvement stores.

Muriatic acid can be used on outdoor floors to clean the toughest stains, like rust or dried grout. It’s a powerful, toxic material that should be used with extreme caution. Wear protective eyewear and gloves when using it and be sure to follow manufacturer instructions on how to clean concrete with muriatic acid.

For indoor concrete floors that are polished or stamped, you’ll need to take a gentler approach to how to clean it. You’ll just use a mop and a bucket of water mixed with a mild cleaner. Don’t use ammonia, bleach or any highly acidic substance on polished or stamped floors. Some good cleaners include Castile soap, liquid dish detergent, stone cleaners and mild floor cleaners. Mix a solution, apply to floor with a wet mop and then rinse with a mop dipped in clean water.

Apply a Sealer

To make your concrete floors resistant to future stains, apply a concrete sealant. Use a paint roller to apply it to clean, primed concrete. Start in the middle of the area and roll the sealant out to the edges. Floors need to be resealed every two to three years. Knowing how to clean concrete properly will keep the floors in your garage, workshop and house looking good as new.

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