rando q - removing rust from concrete?

[psomero]

Bought a big chunk of durabar round, approx 9" OD x 2" thick. Bandsawed out what is going to be my compound eliminator on my 9x20 lathe. Decided "I'll sweep up the chips (dust) in the morning" and naturally it rained that evening.

Now there is an orange/brown streak down my driveway. The dust was about a half inch thick around where the sawing was and I have been chunking out big pieces of rust cake with a cold chisel. Oh, it's been sitting like that for about three months now also.

Any recommendations on how to etch the rust that's stuck on the concrete away? I'm thinking phosphoric acid and a stiff wire brush, but am wondering if anybody else has any other tricks/suggestions. Just picked up a wire cup wheel for my angle grinder and need to attack the big chunks this week. No particular hurry, so if I have to sprinkle something on it every day for the next six months, that's fine.

[Doozer]

Muriatic or phosphoric acid.

-D

[nickel-city-fab]

Dump some cheap (89 cents/2 ltrs) diet cola on it, wait for it to rain again. Repeat as necessary. Old garage trick. I would *NOT* use muriatic on concrete if you value the concrete -- the acid dissolves the lime and you will be taking bids on a new driveway. Just sayin' because I used to work at a cement company a couple decades ago.

[deltap]

Mix iron out to a paste, apply and let sit, rinse, repeat. Pressure washer will remove but will expose the aggregrate.

[J Tiers]

Definitely no strong acids. Even phosphoric is sold as "concrete etch". And that is probably what is in diet Coke.

But, get some "barkeeper's friend". As I recall, that has oxalic acid in it, and that will do a decent job of removing the rust stains without doing too much damage.

[lakeside53]

yes, oxalic acid - gone instantly. Also found in some "wood brighteners".

[mickeyf]

Definitely no strong acids. Even phosphoric is sold as "concrete etch". And that is probably what is in diet Coke.

I believe the diet coke stuff is referred to as "tooth etch".

[nickel-city-fab]

I believe the diet coke stuff is referred to as "tooth etch".

AKA "mountain dew mouth".... I've had coworkers who were completely toothless by age 45

[Baz]

A common misunderstanding about cola. It is PH7 ie neutral. A question was famously aked in the UK parliament about it in the fifties. The feeling that it is attacking your teeth is the effect of the CO2 bubbles cleaning your theeth, like denture cleaner. However later the sugar does turn to acid.......

[metalmagpie]

Coke would be carbonic acid.

[J Tiers]

Some sodas DO have phosphoric in them. Not a lot, but it is there for "tartness", which generally means somewhat acidic.

[nickel-city-fab]

Some sodas DO have phosphoric in them. Not a lot, but it is there for "tartness", which generally means somewhat acidic.

It helps if people read the fine print AKA "the ingredients". Most every cola that I have ever seen, has a bit of phosphoric in it.

[Galaxie]

yes, oxalic acid - gone instantly. Also found in some "wood brighteners".

Yep, a.k.a "wood bleach"

[MrWhoopee]

C02 dissolved in water is carbonic acid. It's how rainwater slowly dissolves limestone, forming caves. Then there's the added phosphoric acid...

[JRouche]

Muriatic or phosphoric acid.

-D

Yup, muriatic acid for concrete rust. He is correct. JR