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Few stains can ruin the appearance of a beautiful concrete driveway, patio, garage floor or other exterior concrete surface more than rust. Not only are rust stains an eyesore, they can be difficult to eradicate because they often penetrate into the pores of the concrete. The good news is that you can remove most rust stains by using the right type of cleaning agent and a bit of elbow grease. Here’s a look at the most common sources of rust stains, the best methods to use to remove them, and tips for keeping your concrete rust-free.

Sources of rust stains on concrete

Rust stains on concrete can come from a variety of sources, some obvious and some that may surprise you. In all cases, the culprit is some type of metal (particularly iron) that has been exposed to the elements and comes in contact with your concrete.

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The most common sources include metal patio furniture, rusty garden tools, metal fence posts, iron railings, and lawn and garden fertilizers that contain certain metals and minerals. But it’s also possible for rust stains to originate from within the concrete itself. If steel rebar or wire mesh embedded in the concrete becomes exposed to air and moisture because of cracking or damage to the concrete, rust will form and make its way to the surface. The aggregate within the concrete may also contain small amounts of iron that could become exposed as the concrete wears.

Before you attempt to remove any rust stains on your concrete, be sure to identify the root cause. Unless you eliminate the source, the stains are likely to reappear and all your cleaning efforts will be wasted.

What are the best rust removers for concrete?

Unlike many other stains on concrete, rust can’t be removed by using common detergents and pressure washing alone. To remove most rust stains, you need to use an acid-based cleaner that will dissolve the rust. This can range from simple household products such as lemon juice or vinegar to powerful chemical cleaners that contain oxalic acid or trisodium phosphate.

The product you choose often depends on the age of the stain, how extensive it is, and the porosity of the concrete surface. No matter what method you use, the sooner you tackle the rust stain, the easier it will be to remove.

Using home remedies to remove rust stains

For newer rust stains that haven’t penetrated into the concrete, you can often remove them successfully by using natural acidic cleaners found around the home. Lemon juice and white vinegar are both great options, but even Coca-Cola can remove minor rust stains on concrete because of its high phosphoric acid content.

Steps for removing rust on concrete with lemon juice or vinegar:

  1. Start with a clean surface so the acid can fully penetrate
  2. Then pour the liquid, undiluted, directly onto the rust stain
  3. Allow it to sit for at least 10 minutes
  4. Then scrub the stain away with a stiff-bristled brush
  5. Finish by rinsing with warm, soapy water

Tip: White vinegar has a slightly higher acid content than lemon juice and may work better on some rust stains.

Using chemical cleaners to remove rust stains

If you are unable to remove rust stains using the methods above, you’ll need to resort to a stronger chemical rust remover for concrete, which you can purchase at most home improvement stores. Many of these commercial rust removers contain oxalic acid, a powerful cleaner that can remove even the toughest stains. Trisodium phosphate, when diluted with water, can also be very effective.

Make sure the surface is clean, apply the rust remover following the instructions on the container, and then scrub and rinse. For deeper stains, give the cleaner time to penetrate into the concrete and then use a pressure washer to rinse it off the surface.

When working with chemical cleaners, it’s important to take the proper safety precautions, including wearing gloves and safety goggles and working in a well-ventilated area. These strong acids can also strip concrete stains and coatings from the surface, so be prepared to do some touch-up work after the rust stains are removed.

As an alternative to using harsh chemical rust removers, look for a natural acid-based cleaner formulated for concrete, such as 720ES Exterior Surface Cleaner from Franmar. These cleaners are good for removing light surface rust and are often safer to apply.

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Can I use CLR to remove rust on concrete?

CLR® (short for calcium, lime, rust) is generally safe and effective at removing rust stains from concrete and is readily available at any hardware store. Its active ingredients (lactic and gluconic acids) are less caustic than harsher acid-based cleaners yet potent enough to quickly remove rust from a variety of surfaces.

However, keep in mind that CLR is not specifically formulated for use on concrete and the manufacturer advises against using it on colored, coated or sealed concrete or on new concrete that’s less than a year old. It’s always best to test CLR on an inconspicuous area of the concrete first to make sure there is no unwanted reaction.

What to do once the rust is gone

If you were able to remove the rust, but now you’re left with a discolored spot, you can use concrete coloring or concrete resurfacing to remedy the issue.

Tips for preventing rust stains on concrete

The best way to prevent rust stains on your concrete is to keep it sealed and repair any large cracks that could allow water to penetrate down to the rebar. Also take these other prevention measures:

  • Immediately sweep off granular fertilizers that come in contact with the concrete. The metals found in fertilizer can start rusting in as little as a day once exposed to moisture.
  • Remove any rustable metal objects from the concrete that aren’t coated or painted.
  • Apply a rust-preventive paint or coating to metal patio furniture or other metal decorations or hardware that you can’t or don’t want to move.

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