Removing Rust Stains From a Brick Chimney

Had a customer tell me he tried muriatic acid and it didnt even touch it… makes me wonder if oxalic acid probably wouldnt even touch it either… Figured I’d come to the greatest peanut gallery of all time for some guidance !!! any ideas guys ?

dont trust what the customer says. Do a test on your own with F9 barc or whatever rust removing chemical you have.


Hey! Can’t help much with the official technique since I’m just starting. I helped a buddy clean the siding of his house before, which had brick trim and he had an old cast iron pipe in one section that was mixing with moisture and running down the side to the concrete. Honestly I put CLR (the most commercial you can get) on it and let it sit before pressure washing. It worked decently and he removed the pipe because it was old contruction and not used. Maybe the customer didn’t lrt their product sit or it was diluted incorrectly? Looking at the photo it looks like the cap on top of the chimney is rusted and just running down. Are you able to test a spot and then come back to pretreat and wash?

Slow your roll there, amigo. CLR is not going to touch a stain like that and I doubt it can be purchased in the quantities that this stain will require.

You can do a test spot with OA, F9, etc. No problems there.

But, what you need to figure out is what is being done to prevent the stain from returning. Have the customer address that prior to you cleaning it and you’ll be golden.

I’d bet a couple pennies that OA will lighten it significantly but not remove it altogether. I’d start with that and just keep misting it down with 12v for about half an hour. Then wash thoroughly. Then step up to F9. If those two combined won’t take care of it then you may have to step up to something stronger. What that might be, I don’t know.

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That white area at the Chimney top, looks etched to me…muratic or any acid, will do that if it’s not rinsed out.
I’m betting he did try muratic and didn’t clean it off the clay brick properly. There’s no way to fix that! That being said we use onerestore, 1 application, high pressure rinse and it comes right off for rust or calcium stains on brick.

That’s a $600 job at least - that’s a 30’ tall chimney and a good chance you could drop $200 in chem on it. I’d give him an estimate of $700-800 to see if he really wants it cleaned before you spend much time even worrying about. People always want their chimneys cleaned but don’t want to pay squat for it.


Hahaha. I know, I was just giving an example of what a consumer would use or how they would use it. Sort of a wax on wax off solution instead of letting a solution do its job, commercial grade or not. Wasn’t trying to give bad advice. My bad. Just pointing out that usually the metal cap on the top of the flue is probably the source of the rust color stain and that is the source. Like you pointed out, it should probably be replaced like my buddy did with the cast iron pipe.

I agree…I doubt seriously if he wants it cleaned bad enough to pay for it…and I am not sure that I would even do it. If he did agree to pay your price, he would want it perfect and I don’t think that one will clean up perfectly. Sometimes, that brick just will not give up what is on it…short of standing there 2 days and messing with it. It is just not worth it to me for the potential hassle.

This is one of the best things I have learned from this forum over the years, now when I see a job like that I instantly think how many simple houses could I go wash and not have to worry about this mess?

Like has been said, lots of chemical, lots of time and it still may not work great, if they are willing to pay a premium price or they are a great customer, maybe I would fool with it. But if not let someone else deal with that headache.

When I started I never wanted to turn down a job or admit defeat. Now I just smile and say “I can’t really do much with that, sorry” and move on down the road. The temptation is there to do it when you are hungry but half of those jobs come back to bite you anyway.

I hope it works out for you.



Well put Joe.


I would bet you they sprayed chemical on that brick dry. Soak that thing down once the brick is satisfied then apply your chemicals I would start with ox acid it may take a few treatments and some scrubbing but it will come off. I would definitely set expectations low and bill accordingly. You never know unless you try

You and racer had the best answers lol. I thank everyone however for helping to reach that general consensus. I know what I must do haha…

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Sounds bad but walk away haha

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Yes Barc is great I also use vinegar, it cost less

:rofl: :rofl: :rofl: If you can get vinegar to work as well as F9 Barc you must be a magician.

Get Craig’s F9 Cookbook - it has detailed instructions on how to tackle stuff like that. You should keep in mind though that is a really more of a restoration than a cleaning. I can easily see three different processes being needed to bring that back to looking good, Efflo, BARC, and Double Eagle + SH


did I say it works as well ? Sorry Barc is great and yes I can get vinegar to work on rust as well as other stains… Thanks for asking

Didn’t mean to come off as a jerk so I apologize for that. I honestly thought you were joking just because there’s such a huge difference between F9 Barc and even Oxalic Acid which a lot stronger than vinegar. Vinegar is just so weak I was just surprised to see it mentioned for rust removal and there are other options that are just as cheap. Oxalic does okay on newer rust but, if you try it on older rust, it just takes too long due to the multiple applications it takes. It still won’t remove really bad rust. I always start off with it and try unless I know it won’t touch it.

No worries, but you are right , not near the F9 product (vinegar) I do work for home builders and sometimes there will be rust stains from nails on driveway Barc is a beast !! and sometimes I can get 90 % of light rust up pretty good. The Oxalic acid… where can I get that product, and did you mention that it was also pretty inexpensive ? Thank you