Concrete surfaces are found in both commercial and residential spaces. This includes driveways, parking garages, and building walls. While generally easy to maintain, they can develop rust over time, creating not only an unpleasant appearance but also damaging the concrete.
Therefore, it’s always best to get rid of these rust stains as soon as they appear. You can remove rust stains from concrete by first scrubbing and rinsing it with soap and water. You can then apply an acidic rust removal solution, allow it to sit for a few minutes, and then use a pressure washer to remove the solution and rust from the concrete.
In this article, we will go over the detailed steps for removing rust stains from concrete. We’ll also dedicate a section where we discuss some of the things that may cause rust to develop on concrete surfaces and how you can prevent them from happening.
What You Will Need
To effectively remove rust stains, you should have the following:
- Pressure washer (such as the Sun Joe SPX3000)
- Liquid detergent
- Lemon juice (for minor stains)
- Vinegar (for minor stains)
- Rust cleaner (for tougher stains)
- Rubber gloves
- Safety glasses
- Steel-toe boots
What Causes Rust Stains on Concrete?
Before starting the cleaning process, it’s good practice to first understand what causes rust stains on concrete surfaces, so that you can prevent this from occurring again.
Rust can form on concrete surfaces in many different ways. This includes contact with fertilizers or rusty garden tools. If the concrete is cracked or damaged, the steel rebar or wire embedded inside may develop rust when exposed to air and water.
This rust will then work its way toward the surface where it becomes visible. It’s also important to note that some causes such as snow or ice coming in contact with the concrete tend to be unavoidable. The different factors that can cause rust stains on concrete are described below.
Minerals dissolved in water can cause rust to develop if this water gets onto the concrete surface. This includes minerals such as sulfates, magnesium, and chlorides. These minerals are typically found in deicing salts, salt water, and well water.
Snow and Ice
Snow and ice can also leave behind minerals once they melt. These minerals can then cause rust stains. While cleaning the concrete surface regularly may temporarily prevent this, in some occasions it may be unavoidable (especially for older concrete driveways).
Acidic solutions from wet road salt or battery acid can cause rust stains on concrete.
Iron oxide forms rust when it comes in contact with water. This compound is present in the soil and equipment. If either of these is left on the concrete surface, they can transfer rust to it.
Rusty objects can transfer the rust from their surface onto concrete surfaces if they are left on them for prolonged periods. This includes rust from tools, machinery, equipment, and vehicles, to name a few.
1. Prepare the Surrounding Areas
It’s important to prepare the area surrounding the rusty concrete before starting the cleaning process, this includes removing items that could get damaged by the acidic cleaning solution or the high-velocity water spray from the pressure washer.
If there are certain objects or areas you wish to protect without having to remove them, use a tarp to cover them, and consider taping the tarp down to prevent water from getting in.
Also, be sure to cover any exposed electrical outlets using tape or tarp, if water gets into electrical outlets, it could cause water damage, short-circuiting, and even electrical fires. Light fixtures can also get damaged even if you cover them up with duct tape or tarp, avoid aiming the power washer at light fixtures to prevent damage.
2. Prepare the Concrete for Rust Removal
The next step after preparing the surrounding areas is to now prepare the concrete for rust removal. To do this, you must first clean the surface to get rid of any dust, dirt, or debris, and pay attention to any cracks and pores on the concrete as well.
This is because debris creates a barrier between the rusted concrete and the rust removal solution. Strong streams from the pressure washer can cause injuries, therefore it is encouraged to wear protective equipment such as safety goggles, waterproof gloves, and boots, before using the pressure washer.
In addition, when it comes to dealing with rust, we recommend using a respirator as rust can irritate the eyes, nose, and throat when it gets in the air.
We recommend adding detergent to your pressure washer’s detergent tank and using the washer with a low-pressure nozzle to apply the detergent to the concrete’s surfaces. Be sure to use recommended cleaners that suit your pressure washer’s detergent tank.
To rinse off the detergent, use a 25°-40° pressure washer nozzle tip. Better yet, use a pressure washer surface cleaner if you have one. A surface cleaner attachment is great at covering large surface areas for more efficient cleaning without damaging the concrete. Avoid using a strong nozzle tip.
When in doubt, perform a patch test on a small inconspicuous part of the concrete to determine whether the chosen nozzle tip is a suitable choice before proceeding to rinse the rest of the area.
3. Apply the Rust Removal Solution
Now that the debris has been cleared away, the rust can be properly tackled by applying an appropriate rust removal solution. This will depend on the severity of the rust stains which we will go through in detail below.
Minor rust stains are generally lighter and confined to small areas. Tougher rust stains tend to be dark and cover a much larger area on the concrete’s surface. Bear in mind that harsh rust removal solutions can be strong enough to cause damage to the concrete.
A patch test is always recommended to determine its effectiveness before applying it to the rest of the rust-stained areas.
For Minor Rust Stains
Lemon juice and white vinegar are great for removing minor rust stains. Below, you’ll find out why they are effective and how you can prepare the cleaning solution:
- Lemon Juice – Lemon juice is a natural and organic acidic solvent that can dissolve minor rust stains. The acidity of the lemon juice reacts with the rust, softening and dissolving the deposits. Apply lemon juice by juicing a cup’s worth of juice and pouring it on the affected areas or sprinkle salt generously on halved lemons and rub it into the rust. Allow the lemon juice to sit for 15 minutes.
- White Vinegar – White vinegar is another cleaning solvent you likely already have at home. This solvent is stronger than lemon juice, making it better at cleaning deeper rust stains. To apply this solvent, you simply need to pour it over the affected rust area and allow it to sit for 10 minutes.
For Major Rust Stains
For tackling major rust stains, we recommend using either hydrochloric acid or a cleaner that is formulated to remove rust, such as the Iron OUT Liquid Rust Stain Remover, which works well on outdoor concrete surfaces.
- Rust Stain Remover – You can remove major rust stains from concrete using a dedicated rust stain remover. Outdoor formulas don’t require any scrubbing and are generally safe to use around vegetation. However, because the product contains harsh chemicals, be sure to avoid breathing it in and use chemical-resistant gloves and eye protection. Follow the instructions on the dedicated rust stain remover to tackle major rust stains on the concrete, the solution can be applied using a tank sprayer, cloth, sponge, brush, or roller. Observe and rinse once the stain has disappeared, allowing the harsh solution to sit longer than necessary may cause further damage.
- Hydrochloric Acid – If your concrete rust stain problem is especially extreme, you can use hydrochloric acid to remove the stain. However, this should be avoided unless there is no other option. This is because hydrochloric acid can stain concrete and cause it to turn blue if it is left on for too long. To use hydrochloric acid for rust removal, start by combining 2 cups of hydrochloric acid with 1 cup of water in a bucket. Pour the solution onto the rust stain and allow it to sit for 5 to 10 minutes. Avoid letting the solution sit for any longer as it will stain the concrete surface.
4. Rinse With a Pressure Washer
After letting the rust removal solution soak for the necessary amount of time, it needs to then be thoroughly rinsed using the power washer. This also eliminates the need for scrubbing during the rinsing process. Use a 25° nozzle tip to get into the pores of the concrete surface without damaging it.
Once attached, maintain a six feet distance and aim the pressure washer wand directly at the concrete, working from top to bottom, from left to right to prevent streaking. If any stains remain after the power washing, repeat the rust removal solution application step.
You can also try using a stiff-bristled nylon brush to scrub the stain after applying the solution to work it into the rust. A nylon brush is best for this purpose as it is stiff enough to remove solids without damaging the concrete. Avoid using metal brushes as the metal bristles will scratch the concrete.
5. Apply Protective Sealant (Optional)
You can reduce the likelihood of your concrete surface developing rust stains in the future by applying a sealant layer to it following the rust removal process. There are several sealants currently available on the market. We recommend the following” products:
- Acrylic Concrete Sealer – An acrylic concrete sealer is perfect if you want to leave your concrete with a clear look. It takes only a short while to dry and is chemical stain-resistant, scratch-resistant, and weather-resistant. You can apply this sealer by first etching the concrete surface using an acid solution and then spraying the product evenly over the concrete. Leave it to dry for an hour and apply a second coat. Allow the sealer to dry properly before using the concrete surface.
- Eco-Friendly Concrete Sealer – An Eco-Friendly Concrete Sealer is non-toxic and non-flammable. This allows it to protect your concrete surfaces from weather and other elements without damaging your landscaping. Similar to the acrylic concrete sealer, you can apply this sealer using the spray-on application method. This sealer dries with a clear finish rather than a wet and glossy look. To apply this sealant, start with a dry and clean concrete surface. Next, load the sealer into a pump sprayer and apply an even layer across the concrete surface. Finally, wait two hours for the product to dry.
Sirinan is a self-proclaimed cleanaholic and the editor-in-chief of Cleaney. Apart from coming with up creative ways to keep her living spaces clean and tidy, she loves to read on rainy days.