Howdy! I’m back with a couple more questions–this time on rust removal. I have searched the board extensively and I believe I have found the general consensus on how to approach concrete rust removal. Please advise me if I have anything wrong or if you have any helpful tips I would love to hear them. I have attached a few pictures of a job I have been asked to bid.
Here’s what I’m thinking: Pretreat everything with HW mix and let dwell maybe 20 minutes. Surface clean and rinse. Mix 1CUP/GAL of Oxalic acid and mop onto rust stains. Agitate with stiff bristled brush and let dwell. Rinse.
OR
Buy F9 BARC (if customer is willing to pay a significantly higher price) and follow nearly the same process.
Which would be better? What can I do to prevent killing the grass and nearby plants? As always, any help is greatly appreciated!
I hadn’t considered tannin stains but they do look very similar. I did a test on one of the sidewalk portions with 1/2 CUP Oxalic acid to 1 GAL water and applied with a pump sprayer. I let it dwell about 10 minutes then washed with a turbo nozzle and applied again and after about 20 minutes it still looked the same. I just bought the OA a few days ago though I have no idea how fresh it is.
The spots may be tanning but most likely fertilizer from the lawn guy. I can tell you after doing miles and miles and miles of rust removal every year the application that has always worked best for me is 1 lbs of OX per 4 gallons of water apply very heavy so it soaks in deep or the stain may come back the next day. Don’t prewet and no rinsing. Spot sprayers don’t put out enough in my opinion. A 12volt system or air system works well . I never used f9 I would never pay that kind of money to replace someone that already works. Nor would you ever catch me using a mop or brush way to time consuming
Never really had any problems. But every area is different. I can’t say how sensitive the plants and sod are in your area. I just know it doesn’t effect them here
I agree its fertilizer. Specifically the iron. Ironite will really do a number on concrete. Just spraying ox and water at 1c:1 gallon will get rid of it without agitation needed.
You can easily stop that with a rinse once the rust is gone. Very important when doing it on stucco houses. Stop the action as soon as the rust stain is gone with dilution. Or you can spray the whole thing taking care not to over spray. Im not sure what it does to grass because Ive never sprayed the grass.
Okay, great. I went back today to recheck the test spot I did and the 1/2 CUP to 1 GAL mix actually did lighten the stains by probably 70% with the remaining spots being where the fertilizer obviously hit directly and soaked in. I’ll be sending my bid and hopefully they will go for it.
What would be the preferred way to apply? I have a 2 GAL pump sprayer now but I need to build a 12v system ASAP so I may do that if the results will be significantly better or if the amount of time is drastically reduced. I’ve seen @squidskc has had great results on some siding and a parking lot with a pump sprayer on a cart I believe.
The first picture is the very next slab of concrete and the bottom is the slab I tested. They were very similar before the application but I forgot to get a before picture of the title I actually tested.
I know that others in this situation have had good results applying the mix from a bucket with a paint roller on a pole. Seems effective for even coverage and no worries about grass
@displacedtexan, rolling on oxalic on concrete is actually most effective in my experience. Not too much more time consuming and better finished product in my opinion. I’ve actually logged out of the forum with no real intention of returning. This came through to my email, but PM me and I’ll send you my contact info if you have any questions.
