ᐅ Removing Rust Stains from Concrete Patio Slabs

Good morning,

we have a big problem.
We have some rust stains on our patio slabs, which are made of simple concrete pavers.

How and with what can we remove the rust stains?
Can you recommend a cleaner or a good household remedy?

The rust stains were caused by an iron-containing lawn fertilizer that spilled onto the patio, and we didn’t clean it up or didn’t notice it.

How would you proceed?

Since I assume the stains are already a few days old, I would recommend using a specialized product (these usually contain oxalic acid). For example, products from Lithofin or Mellerud, just to name a couple commonly found in hardware stores. There are certainly dozens of smaller specialist suppliers as well.

For very fresh stains, you can treat them with citric acid (lemon juice) and salt. This is a traditional home remedy.

@nordanney We have 1-2 spots that are older (we didn’t know where they came from), and now, from yesterday to today, we have many spots and realize they come from the fertilizer (had never thought of that).

Do you think we should first try using citric acid (citric acid concentrate from the lemon bottle)?
Does the citric acid not damage the stone?

Or should we go straight to something like Mellerud?

First, try a home remedy. Mix lemon juice (or better yet, powdered citric acid) with salt to form a paste. Apply it to the surface and let it work for 1-2 hours. Then scrub it off and rinse. Since the mixture is quite mild, the stone won’t be damaged. The acid reacts with the rust. You can look it up to learn more about the chemical reaction. This is something taught in high school chemistry.

If it works, great. Otherwise, head to the hardware store. Stronger products contain harsher acids. Therefore, citric acid is a gentle starting point and not harmful.

@nordanney I just read about this as well. Ascorbic acid, which is Vitamin C, is supposed to work too.

In what ratio should citric acid and salt be applied to the stain? Then probably moisten it and let it sit?

FrankChief schrieb:

What ratio should lemon acid and salt be applied to the stain?

I only know it from practical experience. Mix powdered citric acid with water until you get a mushy consistency. Then add salt until it becomes a thick paste. I have no idea about the exact ratio. It doesn’t really matter.

FrankChief schrieb:

Ascorbic acid is said to work too; that’s vitamin C.

It works chemically with all acids, including highly concentrated hydrochloric acid or similar. However, the stronger the acid, the more likely it is to damage the stone.