Depends on what caused the stain. Most every rust treating product contains some oxalic acid. Pure oxalic is available in industrial size qty. so you will have to find a professional pressure cleaning company that uses it if the store bought product is not strong enough. Rust stains caused by battery leaks and fertilizers can be especially difficult. When in doubt, call a pro!
Thanks Steve! I planted my Herb Garden in a red wagon and it rusted so it's metal rust.
Try using the product AWESOME you can find it in your local Dollar Stores. I use it on every rust stain that I have even indoors and it is amazing.
Thanks Beth. I actually have that and I use it to remove paint. I will give it a try.
You may need to use muriatic acid to remove this stain. Be careful and use gloves and eye protection. Try a small out of the way spot to assure it will not discolor the cement. It tends to make the cement white so the results may be worse then the stain. But acid is used all the time to remove stains on cement products. Also once done regardless of what you end up using, be sure to flood the area well with water or it can have bad results with grass and plants if its gets onto the lawn or garden.
add some bleach