How to Remove Rust from Concrete

Rust stains on concrete surfaces can be truly unsightly. They are mainly characterized by their yellow to earthy orange color, and can be caused by a variety of reasons. However, their removal is not quite simple, and thus basic methods, such as pressure washing, are not usually effective.

In this article, we will address different methods on how to remove rust stains from concrete, using different materials and techniques ranging from home remedies with household products to special proprietary chemicals. But first, let us explain the main causes for rust stains.

What causes rust stains?

There are various causes for rusts stains on concrete surfaces, which can be mainly categorized into external and internal. External causes include the exposure to curing water that contains iron oxides, red clay soils, fertilizers, rusty objects, etc. Whereas, internal causes include certain types of aggregates which contain iron oxides, and corrosion of steel reinforcements.

The ideal rust removal methods

Rust stains can vary from being light and new to deep and old. Accordingly, we will address different removal or cleaning methods depending on the type of the rust stain.

Method #1: How to remove light and relatively new surface rust stains using home remedies

The home remedies for the removal of rust stains from concrete involve the use of common household products. Usually, this method is simple yet effective for the light and fairly new rust stains. Besides, we recommend performing a test on a small area first.

Things you will need

• Safety gear.
• Coca Cola / lemon juice / white vinegar / tri-sodium phosphate (TSP).
• Bristle brush.
• Soap.
• Clean water.

Notes

• Trisodium Phosphate: Other names include Sodium Orthophosphate, TSP, or Phosphate of Soda.
  Appearance: White crystalline odorless powder.
  Availability: It is available at the supermarkets.
  Hazards: This product is corrosive to flesh.

Steps

1. Wear your safety gear.
2. Apply one of the following solutions to the rust stains:
   • Coca Cola.
   • Lemon juice.
   • White vinegar.
   • TSP solution.
3. Let the solution stand for 10 minutes.
4. Scrub the stains with a bristle brush to loosen up the rust.
5. Rinse with clean water.
6. Re-scrub with soapy water.
7. Rinse and flush thoroughly.

Explanation

This method is quite simple and straight forward. First, after wearing your safety gear, apply a generous amount of Coca Cola, lemon juice, white vinegar, or a TSP solution according to the product’s dosage right on the rust stains. After about ten minutes, scrub the spots using a bristle brush. In this step, you can apply additional solution while scrubbing if needed. Then, rinse the surface and re-scrub with soapy water. And finally, hose off and flush the surface a couple of times with clean water.

Method #2: How to remove light surface rust stains from concrete using mild acidic solutions

This method is highly effective for the removal of light surface rust stains from concrete, and involves the use of weak or diluted acids. However, we recommend testing this method on a small hidden area first.

Things you will need

• Safety gear.
• Bristle brush.
• Mop.
• Oxalic acid / phosphoric acid.
• Stiff bristle broom.
• Baking soda.
• Clean water.

Notes

• Oxalic acid or Othanedioic acid.
  Appearance: Colorless crystalline compound.
  Availability: It is available at cleaning and chemical supply stores.
  Hazards: This product is toxic, irritant, and corrosive to flesh.
• Phosphoric acid or Orthophosphoric acid.
  Appearance: Colorless granular solid (pure), or clear liquid (diluted or less concentrated).
  Availability: It is available at chemical supply stores.
  Hazards: This acid is toxic, irritant, and corrosive to flesh.

Note: Always add acid to water and not water to acid.

Steps

1. Wear your safety gear.
2. Gently scrub using a bristle brush to remove the rust stains, if possible.
3. Prepare the acidic solution, which consists of a 10% solution (1 part acid to 9 parts water) of one of the following acids: oxalic or phosphoric.
4. Mop the surface with the solution.
5. Let it stand for about 2 hours.
6. Rinse and flush the surface with clean water while gently scrubbing it with a bristle broom.
7. Neutralize the surface with 1:10 baking soda to water solution.
8. Flush thoroughly with clean water.
9. Repeat as needed.

Explanation

First, put on your protective gear especially that you are working with acids. Then, gently try to scrub off as much as possible of the rust stains using a bristle brush. Next, prepare the 10% acidic solution by diluting one of the acids (oxalic or phosphoric) with water. Here, it is important to add the acid to the water, and not the water to the acid. Besides, if you have the acid in an already diluted form, check its concentration and dilute it further to reach the desired 10% value.

Then, mop the surface with this solution, and let it stand for 2 hours. Next, rinse and flush the surface with clean water while gently scrubbing the stains with a bristle broom to loosen them up. Then, neutralize the surface with a solution of 1 part baking soda to 10 parts water, while brushing it and letting it stand for 10 minutes. And finally, flush the surface thoroughly with clean water.

Method #3: How to remove moderate to stubborn rust stains using proprietary products

Using a proprietary product can be really effective for the removal of moderate to stubborn rust stains from concrete. However, there are plenty of products in the market, and not all are similarly effective. In addition, the application of the proprietary products may vary between one and another, however, we will briefly address the typical procedure.

Things you will need

• Safety gear.
• Bristle brush.
• Proprietary rust remover.
• Clean water.

Steps

1. Put on your safety gear.
2. Apply the product to the stain.
3. Let it stand for a certain period of time.
4. Scrub using a bristle brush.
5. Rinse with clean water.

Explanation

The typical method for the application of a concrete rust remover simply includes the application of the product, waiting time, scrubbing, and rinsing. Besides, products come in different forms, either being liquids, powders, or gels. In addition, some are ready to use, whereas others may require dilution or mixing with water.

Method #4: How to remove deep and stubborn rust stains from concrete using a poultice

One of the most effective methods for the removal of deep and stubborn rust stains from concrete is through the application of a poultice.

Things you will need

• Safety gear.
• Sawdust / cat litter / calcium carbonate powder / talc.
• Sodium citrate / ammonium citrate.
• Warm water.
• Stiff bristle brush.
• Soap.
• Clean water.

Notes

• Sodium Citrate, Tri-sodium Citrate, or Citrate of Soda.
  Appearance: White crystalline compound or powder.
  Availability: It is available at chemical supply stores.
  Hazards: None.
• Ammonium Citrate, Citric Acid, or Di-ammonium Salt.
  Appearance: White crystalline compound.
  Availability: It is available at the supermarkets, hardware stores, and chemical supply centers.
  Hazards: None.

Steps

1. Put on your protective gear.
2. Prepare a poultice by mixing calcium carbonate powder with a solution of 1 part of sodium or ammonium citrate and 6 parts of warm water.
3. Apply the poultice to the rust stains, and let it sit until dry.
4. Scrape off the residue.
5. Scrub with warm soapy water using a stiff bristle brush.
6. Rinse and flush thoroughly.

Explanation

After wearing your safety gear, mix 1 part of sodium or ammonium citrate with 6 parts of warm water. Then, mix this solution with talc or calcium carbonate powder to form a thick paste. Next, apply the poultice to the rust stains with a thickness between 1/4 and 1/2 inches (~6-13 mm), covering an area slightly larger than the margins of the stains, and leave until dry. Afterwards, scrape off the remains and gently scrub with warm soapy water, and finish with rinsing and flushing the surface.
Note: for vertical surfaces, this poultice might not be stiff enough to stick. However, you can add 7 parts of glycerin to improve its physical properties to be suitable for vertical surfaces, and can be applied for 2-3 days before removal.

Frequently asked questions

Will WD 40 remove rust from concrete?

WD 40 can be effective in removing relatively new and light rust stains from the surface of concrete. However, for deeper and older stains, you will need to apply certain acids to break down and loosen up the rust, where WD 40 is not truly effective.

Will CLR remove rust from concrete?

Usually, CLR is effective for cleaning and removing some rust stains from concrete. But in general, basic CLR is not designed to be used on concrete surfaces. Thereby, it is important to test this product on a small area first to check its effect.