How To Clean Green Stuff Off Concrete

How to Clean Concrete Floors and Driveways

To clean concrete surfaces safely and effectively, begin with the least toxic cleanser possible and up the ante as needed. Here's how to get the job done.

how to clean concrete

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Before You Begin

The first thing to know about cleaning concrete? You don't need to be delicate. After all, it's one of the most durable building materials used in modern construction. But with its durability comes a stubborn resistance to cleaning, which means that sprucing it up requires some background knowledge, a little homework, and a healthy helping of elbow grease.

Read on for guidance on cleaning concrete as well as some tips on the finer points of working with this rigid, hard-wearing material. The approaches that follow will help you remove ground-in dirt, mildew, spilled paint, and most food stains from concrete.

Cleaning Concrete: 6 Steps to Getting the Job Done

SUPPLIES

This list is a guide to what you might need, not what you will need. The supplies you end up using will be determined by the cleaning approach that's best for your situation.

Garden hose
Broom or leaf blower
Commercial concrete cleaner or trisodium phosphate (TSP)
Stiff bristle brush
Pressure washer
Pressure washer solution for driveways
Muriatic acid
Ammonia
Bucket or spray bottle

STEP 1: Determine the type of finish the concrete has.

Before you can clean concrete, you need to find out what type of finish was applied. For example, it's important to know if the concrete has been sealed and, if so, what type of sealer was used. The methods used to clean unsealed brushed concrete will differ from those for cleaning epoxy-coated concrete.

Pro tip: It's not always easy to determine the type of concrete sealer used, especially when the concrete has weathered. If you can't figure out what was used, don't start cleaning with harsh chemicals like muriatic acid. Instead, start with something a bit milder.

Some of the most common sealers include:

Penetrating sealers
Acrylic sealers
Epoxy coatings
Polyurethane sealers

how to clean concrete

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STEP 2: Prepare the concrete to be cleaned.

The approach you use to clean concrete will depend on whether the concrete is outdoors or inside the home or garage. Some methods are safe to use indoors but might damage grass or plants along sidewalks or driveways. But whether you're working indoors or out, you will have to prepare the area before you start, just as you would if you were painting a concrete floor.

Indoor cleaning projects: Be sure to remove any furniture, tools, housewares, and other items from the concrete surface. You'll be using cleaning solutions, so remove anything that might not be able to stand up to a strong detergent.
Outdoor cleaning projects: Sweep the surface clean with a broom or use a leaf blower to remove dirt, grit, and gravel. If you're working around plants and grass, be sure to soak them well with a garden hose prior to cleaning the concrete, as this will prevent the cleaning solution from penetrating the roots.

STEP 3: Try to clean the concrete using a commercial cleaner or TSP.

The bad news for the fastidious homeowner is that concrete is porous and those tiny voids can harbor dirt, mold, and all kinds of deep, stubborn stains.

Your first step should be to try applying common detergents to the tough stains directly, and scrubbing with a stiff bristle (not wire) brush. But you may not get far.

When cleaning garage floors, be prepared to pull out all the stops. If you're dealing with a concrete garage floor that was exposed to leaky oil pans and transmissions for years, even power washing might not do the trick. You may need to scrub the area with TSP and then hit it with the hose to lift the stains. The same approach applies to driveways, sidewalks, or any other concrete surface that's been exposed to oily substances.

How to Clean Concrete - Painted Garage Floor

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STEP 4: If the concrete is outdoors, try to power wash it.

When it comes to outdoor concrete, the first and easiest approach should be power washing. This cleaning method can penetrate the pores in the concrete and wash out the dirt and grease.

The process isn't too difficult: Simply fill the pressure washer soap reservoir with driveway and concrete cleaner and get to work. Concrete cleaning takes a lot of pressure, so don't be afraid to crank up the pressure washer to about 3,000 psi. If necessary, you can really concentrate the water pressure with a 0-degree nozzle.

How to Clean Concrete - Pressure Washing Concrete

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STEP 5: If all else fails, use muriatic acid to clean the concrete.

As a last resort, try an application of muriatic acid—it's often the silver bullet for cleaning concrete with deeply penetrated oil spots. Muriatic acid can work wonders on filthy concrete, and it can also be very effective at cleaning excess smears of dried mortar and grout, or tackling tough rust stains.

Before you use muriatic acid on concrete, make sure to take extra care prepping your space, and clean up carefully afterward. Start by mixing up a solution of 1 part muriatic acid to 10 parts water in a bucket or spray bottle and soak the stained area. Wait about 10 minutes and then spray the area with a solution of 1 cup of ammonia to 1 gallon of water to neutralize the acid.

Pro tip: You must be extremely cautious with muriatic acid. Don't use this powerful acid unless you absolutely need to. If you do use it, be sure to wear protective gear (including protective clothing), and always follow the manufacturer's directions for dilution.

Step 6: Once the concrete is clean, prevent further staining by applying a concrete sealer or masonry primer and top coat.

A concrete sealer is a reliable option for avoiding stains in the first place. Choose a clear silane- or siloxane-based water-repellent sealer like Rainguard Micro-Seal Penetrating Concrete Sealer, a favorite from our researched guide to the best concrete sealers. If you prefer a wet look, Foundation Armor's AR350 Wet Look Sealer is a good choice. Apply either product with a paint sprayer or roller. You can also acid stain the concrete surface before sealing for an interesting new look.

If you're working on indoor concrete and the damage is so extensive that no amount or intensity of cleaning seems to be doing the trick, consider applying a masonry primer and a masonry top coat to hide the old stains and seal the concrete to prevent further staining.

Final Thoughts

Deciding how to clean concrete in a way that works for you can be a challenge, and some stains are harder to deal with than others. If your concrete surfaces aren't sealed, the tips listed above should be all you need to bring them back to tip-top shape. Once you've got those concrete surfaces clean, be sure to seal them. Sealing will help prevent dirt, grime, and grease from penetrating the pores, making maintenance easier.

how to clean concrete

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FAQs About Cleaning Concrete

We've reviewed the basics on cleaning concrete, but you may have some lingering questions. This section aims to satisfy those queries by answering some of the most frequently asked questions about cleaning concrete.

Q. How do you clean unsealed concrete?

Unsealed concrete can be difficult to clean. Start with a commercial cleanser and a scrub brush. If that doesn't work, try a solution of trisodium phosphate (TSP), or give power washing a try. If nothing else works, resort to muriatic acid.

Q. Can you clean concrete with vinegar?

Scrubbing certain concrete stains with vinegar is an excellent and eco-friendly way to clean concrete. Vinegar is especially useful for removing rust stains, although it might not work particularly well for grease and oil. Simply pour diluted vinegar on the stain and allow it to soak in for 15 to 20 minutes before scrubbing with a stiff brush. Rinse the area afterward.

Q. How do you clean bird poop off concrete?

The secret ingredient in a homemade bird poop removal solution is liquid dishwashing detergent. Mix a spoonful of detergent with a spoon of white vinegar and 2 cups of water. Soak the pooped-upon area with the solution, let it sit for 15 minutes, and scrub it clean with a brush. Flush the area with fresh water when finished.

Q. How many psi are needed to clean concrete with a pressure washer?

Concrete's a tough, durable material, and it takes some serious pressure to blast those stains out of its pores. Don't be afraid to crank the pressure washer up to around 3,000 psi and swap in the 0-degree nozzle for stubborn stains.

Q. Should I avoid using a pressure washer indoors?

Just as there are many things you should never pressure wash, there are a number of reasons you shouldn't use a pressure washer indoors:

Spraying electrical fixtures accidentally can be dangerous.
Flooring, drywall, and other surfaces aren't waterproof.
Most pressure washers are gas powered, which means you'd be filling your home with carbon monoxide while you're spraying away.