Oxalic Acid Part 2


I wanted to start a new thread to discuss using OA.

Yesterday I had a great oppotunity to play around with a job that was 4000 sq ft of rust stained concrete (fire water system release drains come out of side of building. Code required iron pipes and when system gets tested, they flush out the lines which causes massive amounts of iron filled water to come pouring out onto a large concrete area).
Using Hot Water I was able to get about 50% of the rust off and then using OA was able to fully remove the remainder of the rust.

I took this opportunity to better understand OA and how it works. We all know it is a good rust remover and concrete brightener.
I used 1/2 cup OA per gal of water (3.33% final solution). It did its thing, removing or reducing the appearance of rust and whitening the concrete.
I then used 1 cup OA per gal of water (6.66% final solution) and did not seem to notice any significant difference in rust removal or level of whitening.
Next I used 2 cup OA per gal of water (12.66% final solution) and it performed much the same as the 1/2 cup OA recipe.

At this point, at least with concrete, I am not able to see how increasing strength of solution seems to have any increased effect on the results. I found having to reapply multiple applications regardless of strength to fully remove the rust in certain areas.

It was getting late and starting to get dark, but my test today is to vary the application methods between a misting of the surface to a heavy pooling and see if extending the dwell time without evaporation has a direct impact on the results.

It is interesting to note that OA does whiten concrete. When applying to 20 year old concrete it was inconsistent in the overall appearance (some spots whiter while other not so much). With 20 year old concrete there are a lot of variations in the surface - I can see lines where someone went to town with high pressure eating away 1/16 of inch of the surface verses other areas that seemed to still have some cream (along edge of building) and everything in between. It appears OA interacts with each “layer” or condition of surface slightly differently.

Does anyone know of a method to take 20 year old concrete with various surface conditions and achieve a more consistent appearance across the entire surface? Muriatic Acid treatment perhaps?




Great test, do you have any pics?

I wonder if running a burnisher with a specific pad would work to even out the surface…