Rust stain question

[JDhomeservices]

Trying to remove this rust stain on a garage floor from a filing cabinet. 12 oz of oxalic in a gallon pump up sprayer didn't faze it, neither did undiluted F9. Never seen a rust stain not budge like this. Any suggestions?

 

[Craig]

Is the concrete sealed? By how dark that stain is it looks like there's a topical. F9 will work as long as it can get to the stain.

 

[Ralph Q]

I have the same problem tried oxalic acid, covered and let it dwell for half an hour. Then scrubbed with a brush. Nothing. I think it is fertilizer stains because the stains are on the edges of the sidewalk. But I know there are sprinklers and this area has hard water. Will F9 take this out?

 

[Craig]

That is some wierd looking concrete. Do you have any more detailed pictures?

 

[Kiloman]

Is that clumped up oxalic acid on the concrete?Looks like some didnt get dissolved.

 

[Ralph Q]

Hi Hal and Craig. No there's nothing on the concrete. I only treated the first section of the sidewalk and as you can see there's no difference at all, on the remaining sections. I don't have any pics that show anything worth seeing. I can say that the other side of the driveway is white and clean with only a faint trace of the brown stain around the edge. And the sidewalk on the side that the pic was taken gets progressively cleaner and brighter and the stains are almost totally faded at the end of the sidewalk. I know they have Chemlawn and I know they have hard water. I would have expected the oxalic to remove at least some of the stain but it didn't even touch it.

 

[Craig]

If its rust, F9 will work.

 

[Ralph Q]

Update: On my sidewalk dilemma

I just wanted to update the progress on the sidewalk I was having trouble with. Apparently I didn't mix the oxalic strong enough. Came out good!! 1st pic is after a minute of spraying the oxalic. second is the final product.

 

[junker1]

well there you go. Another fine job by the pros here on pwi. looks great Ralph Q

 

[Christopher]

How strong did you mix the Oxalic the first time and then the second time?

The later pics look good.

 

[Ralph Q]

I can't remember what I did the first time, I think I had a scooper and just used 1 scoop in quart spray bottle. I thought that would be enough. the second time I just kept adding the oxalic to a quart of hot water until it wouldn't dissolve anymore. that did the trick. it was probably 4 scoops, certainly not scientific, but I guess total saturation is the word for it.