You can remove rust stains from concrete surfaces with these reliable methods
Rust stains can ruin the appeal of a well-kept concrete surface. Unfortunately, they’re not the easiest blemishes to remove since the job requires the right combination of products and techniques. You can learn how to remove rust from concrete surfaces with this step-by-step guide.
Rust occurs when a substance containing iron is exposed to the elements. When this occurs on concrete, which is porous, the stain seeps into the pores of the concrete and causes a stain. There are lots of different ways this can happen:
Garden tools like shovels, clippers, pickaxes, and other items being left on concrete
Patio furniture starting to degrade while sitting on concrete
Old barbecue grills starting to corrode
Wrought-iron railings bolted to concrete surfaces
Also, another common cause is the structural reinforcement inside the concrete. Known as rebar, these iron bars are wired together and embedded in concrete to strengthen it. If the bars are exposed to air and moisture, they can rust from the inside out.
The best idea is to avoid concrete stains in the first place. Protecting the surface with a concrete sealer can help prevent the iron from soaking into the pores and make cleaning up much easier. Learning how to seal concrete isn't all that difficult and can pay dividends down the road.
Regardless of the severity of the stain, it’s a smart idea to remove any surface grease or oil. Grease or oil can prevent the soap from penetrating into the concrete, so you should remove it first. Here’s how to clean concrete with a solution of dish soap and water.
1. Pre-wet the stain with water. This will prevent the concrete from soaking up the soapy water too quickly so it can work on the surface stains.
2. Mix 4 or 5 tablespoons of dish soap with warm water to make a fairly soapy solution.
3. Using the scrub brush, scrub the stained area with the soapy solution. Use alternating patterns, including circular, back and forth, and side to side. Since concrete is so porous, it requires different angles to work the bristles in and loosen up the stain.
4. Rinse the surface well with a garden hose. The stain may be lighter at this point, but the surface-level grease and oil should be gone and allow for direct access to the stain.
Concrete is porous, but those pores are irregular. To ensure the bristles of the scrub brush are able to make their way into the pores and remove stains, it’s important to change the scrubbing pattern. Circular motions and changing between clockwise and counterclockwise are excellent for this, but be sure to change angles as well.
Now that you've prepped the area, the following methods are some of the best ways to remove rust stains from concrete. Which route to choose may depend on the severity of the stain, but for those who aren’t sure how to remove rust from concrete, try them each in order.
Vinegar is an inexpensive and relatively mild acid that can help remove rust stains from concrete. White vinegar is usually best for the job. There is no need to pre-wet the stain after cleaning with the dish soap if you immediately move on to this step.
You’ll need:
White vinegar
Nitrile gloves
Safety glasses
Dish towel
Stiff-bristled brush
Garden hose
1. Vinegar can irritate skin and eyes, so it’s best to don a pair of nitrile gloves and safety glasses to prevent any injuries.
2. Pour the vinegar directly onto the concrete stain. The stain size will determine how much vinegar to use, but be sure to saturate the stain.
3. Immediately cover the stain with a dish towel and pour more vinegar on top to saturate the dish towel. Use enough to ensure the towel is saturated. This will prevent evaporation due to heat or sunlight and allow the acid in the vinegar more time to work.
4. Allow the vinegar to sit for 10 to 20 minutes.
5. Remove the towel and immediately begin scrubbing the stain with a stiff-bristled brush. Remember that it’s important to change scrubbing patterns to ensure the bristles can make it into all the pores in the concrete.
6. Rinse the surface with a garden hose. If the stain is lighter, it may be worth repeating the process. If not, it may be necessary to move on to a more powerful rust cleaner.
Oxalic acid is the main ingredient in most commercially available rust removers. It’s more powerful than vinegar but still a relatively mild acid. That said, it still requires careful use when learning how to remove rust from concrete with these products.
You’ll need:
Rust removal product containing oxalic acid
Safety glasses
Respirator
Chemically resistant gloves
Long-sleeved shirt
Pants
Stiff-bristled brush
Garden hose or pressure washer
1. If there are plants or grass in the area around the stain, soak them with the garden hose. This will help protect the roots from the acid runoff, but it won’t do much to protect the leaves or blades of grass, so be careful when rinsing or spraying.
2. Put on the proper safety gear. Oxalic acid is mild but can cause skin, eye, and airway irritation, so cover up and wear a respirator.
3. Apply the full-strength cleaning solution to the stain, and allow it to sit for up to 10 minutes.
4. Scrub the solution with a stiff-bristled brush. Again, alternate patterns and angles to ensure the bristles reach into the pores as best as possible.
5. Rinse with a garden hose. It may also be worth rinsing with a pressure washer, but use at least a 15-degree nozzle to prevent concrete damage.
If all else fails, bump up the firepower to muriatic acid. Also known as hydrochloric acid, this is powerful stuff, so users should be careful. Again, wear the proper safety gear when using muriatic acid.
You’ll need:
Muriatic or hydrochloric acid
Safety glasses
Respirator
Chemically resistant gloves
Long-sleeved shirt
Pants
Tarp or sheeting
Bucket
Small cup with a handle or large soup spoon
Stiff-bristled brush
Garden hose or pressure washer
1. Again, protect any plants or grass in the area by soaking them with the garden hose, and be careful when rinsing. When using muriatic acid, it may be worth covering surrounding plants with a tarp, plastic sheeting, or another material that can help keep some of the overspray off the plants.
2. Mix a solution no stronger than 1-to-1 water and muriatic solution in a bucket.
3. Use the small cup or soup spoon to apply the water and acid solution to the surface and rust stain.
4. Start scrubbing after no longer than 5 minutes. Scrub for 5 minutes, and then pressure wash the stain. Scrub in different directions and patterns, and be sure to use a nozzle no more aggressive than 15 degrees. Leaving the solution on the surface longer than 10 minutes total can lead to discoloration.
5. Repeat if necessary.
The most important action that a homeowner can take to prevent rust stains from occurring on concrete surfaces is to treat them with a concrete sealer. A concrete sealer will make the porous concrete surface more water- and stain-resistant. This helps by keeping the concrete in good shape so the rebar inside doesn’t rust but also by preventing any rusty stains on top from setting deeply.
It’s also important to change certain behaviors. Parking rusty vehicles on concrete driveways or leaving yard tools in contact with concrete will typically result in some sort of stain, so it’s critical to remove them from the concrete surfaces.
Finally, it’s a wise idea to repair any cracks in the concrete as soon as possible. Cracks occur naturally in concrete surfaces, but they can allow water to penetrate the concrete. This can lead to the rebar being exposed to the elements, rusting from the inside of the slab outward.
Sometimes, the best method to remove rust stains from concrete involves a pressure washer. Their powerful jets can penetrate into the porous concrete and force stain particles, dirt, and other materials out of the pores.
These tools can be helpful. But when used unsafely, they can cause serious damage to both the user and the surface being sprayed. The jets can actually chip small amounts of concrete away from the surface, meaning you might be learning how to dispose of concrete rather than how to clean it. Pressure washers can also easily cut through skin if the user accidentally crosses the stream’s path across their hands or body. For folks who’d rather not tackle this part themselves, there are plenty of local power washing pros for hire.
The best plan for removing rust stains from concrete is to progressively move from weaker cleaners to heavy-duty acids. Move from dish soap to vinegar to oxalic acid to muriatic acid, stopping whenever the stain is sufficiently removed. This process ensures that only the safest possible methods are used, rather than jumping right into a powerful cleaner that may be effective but unsafe and unnecessary
Yes, baking soda and vinegar can remove rust from concrete. Vinegar is acidic and can remove rust stains from concrete on its own. Adding baking soda may increase abrasiveness, which could help loosen some of the stain even more when scrubbing the stain. However, a stiff-bristled brush can do the same.
Yes, pressure washers can remove rust stains from concrete. However, when coupled with an acid treatment, they can be even more effective. Just be sure to use a minimum of a 15-degree nozzle to prevent damage to the surface, and users must also be careful not to get in the way of the pressure washer’s jet as they can cut through skin and cause injury.
