Rusty concrete

[Thomas C]

I have searched the forum on this topic and oxalic acid is the stuff recommended.
I have a driveway with some rust spots. What is the best way to use oxalic acid for this rust. Do I pretreat the spots?
I am a rookie....I admit it..
Thanks you guys

[814jeffw]

That is a really bad looking case of rust. Oxalic may get some out,..but man,..that is bad. Those really dark spots are gonna be a bugger for sure.

[Thomas C]

Thanks Jeff. I was sent over for an estimate by a real estate agent, rust was not mentioned at the time. Bid is not due till Monday.
I would like to get this one as there is more to do if I get this job done.

[PPC]

I would do a test spot with pump up sprayer first 2 cups ox to 1 gallon water or go stronger if need be that still might not work thats why I would do a test spot first good luck

[jetstream1]

That is going to be a hard one good luck

[One Tough Pressure]

Repeated applications of a moderate mix will take care of most of it. Don't overdue it with to strong of a mix and regret it.

[sparkie1]

Safe Restore will remove this rust

[big mike]

I'd stay away from the Safe Restore for that particular driveway. The cement looks fairly new, and it may etch. Try Oxalic, but start out at 8oz per gal. You really don't need a stronger mix, just longer dwell time. Apply then let it dry. Reapply as needed. Should clean up nicely.

[MMI Enterprises]

I agree about being careful..be careful in general if using hydrochloric at strength and for new crete high pressure should be avoided. How old is that concrete? Regardless, if the ox don't work than there will be some etch/damage to be suffered via hydrochloric acid (muriatic) or products containing such whether it new or well cured slab..

Similar issue in this thread: Patina on concrete..

Some Q&A concerning use of hydrochloric as remedy against mineral staining:

What are you applying the 8:1 mix of murrain with ?Sprayer,brush?
Does the bubbling denote the proper dwell time?
Neutralizer left how long?
Finally,will the juice completely lift the stain,then only soft rinse,or should I expect to only weaken the stain,then p/w off.
with my 0 tip.......BWWWWHHHAAAAABWAAAHHH!

The acid bubbling denotes a reaction against a contaminate such as dirt or a mineral. The more it bubbles the more it is eating so be careful. The main strength pretty much plays out when bubbling stops. The 8:1 is but a rough guide and doesn't mean much if say your using a strong or weak version of it. At Osh where I buy it they have two strengths available in different parts of the store. The single gal one is stronger compared to the 2 gal kit. (Kelly Moore has also at the higher concentration)
I apply muriatic anywhere from 4:1 to about 10:1 with mop & bucket or by plastic pump up depending on what I am doing. If I am etching a slab in prep for a solid color coating where visual outcome of the etching is unimportant or doing kitchen tile grout cleaning I apply with mop. Can leave mop trail marks (discoloration) on crete where the mop strands applied more solution if not done real careful to point of flooding. If I am prepping slab for transparent staining or clear coat or removing say a test section of concrete acid stain or need to lighten a too dark acid stain job I spray it on as visually things need to be consistant without streaks. Gotta wear long sleeve clothing, gloves, and eyewear when doing such as all it takes is one little lose fitting or a blown pump cylinder and yer done for.

Far as dwell time..should only take but seconds for it to work unless you got a barrier or seal in the way of the acid. Spray on and as it bubbles for a few seconds brush it around, then rinse.
The stain yer dealing with is an oxidized mineral not much different than when I stain a floor on purpose. The colored particles trapped in the crete pores at the surface will be eaten. The stain probably doesn't really go very deep at all and is probably more particle than part of concrete. Even with the acid staining I do the color is not very deep. Way that works is that the only thing that can react to an acid stain is the free lime that leached up and made contact with oxygen. Can't stain something if it had not gotten air...

Doesn't matter how long a neutralizing agent remains.
Pressure washing probably won't make any difference. There won't be any weakening persay, just a disolving/disappearance of the color. Too much and you will have etched/rough crete. If it goes yellowish from using too much then spray oxalic. That can be left on and whitens as time goes.
A sever case of too strong muriatic where real deep grime or cement glues are leached up turning surface ugly yellow or brown can be fixed by reapplication of same acid but at weaker dilution. Cause being the cure is way that works. What happens is it brings it up but then runs out of power allowing the new stain to sit on top.
Your other options maybe products that use glycolic acid or phosphoric acid such as CLR or perhaps that saferestore stuff.
Again though my fav is the hydrochloric...you'll never find a mason crew or crete guy without a jug of it around.