Homemade Concrete Stain

Failure & Discovery Staining with Manganese

Manganese Chloride is fairly expensive. I decided to save money by buying a cheaper manganese salt and reacting it with Hydrochloric Acid. The first thing I tried was Manganese Oxide, but that was no good because it generated a lot of poisonous chlorine gas that is unbelievably nasty.

Next I tried Manganese Carbonate from a ceramics supply shop. The carbonate was much better because it gave off plain Carbon Dioxide gas and also the reaction is very fast at room temperature. But there was a problem: it stained my spoon but it didn't stain the concrete! Another ingredient was required for success.

I put some Manganese carbonate in a glass bowl and added acid by the teaspoon until the fizzing slowed.
Manganese Carbonate neutralized with Hydrochloric Acid

The solution stained my plastic spoon.
Manganese Chloride stains the plastic spoon

Then I brushed the solution onto the concrete and waited for it to dry. As the solution dried out, the color changed so it was almost exactly the same color of light brown color as the original manganese carbonate powder.
light brown excess crust spread on the concrete

I began to wipe up the excess with a sponge. It was then I discovered that the solution did NOT stain the concrete. Not even a little bit. The dried crust all came up with the sponge, none remained in the floor. I was very disappointed.
it did NOT stain the concrete except along one edge

But there was a silver lining. ... or more accurately a brown lining. The stain actually worked along the border of a neighboring test area. It somehow reacted when it overlapped the other stain. The other stain was made from Copper Sulfate, Sodium Chloride, and Potassium Dichromate. Since the Potassium Dichromate had such a profound effect on the Copper, I guessed that it was the ingredient making the difference between stain and no-stain. I tried adding it and it worked. The specifics are on the regular manganese recipe page.

I'm not sure but I imagine this recipe would also work with other hexavalent chromium compounds like Potassium Chromate, Sodium Chromate, and Sodium Dichromate. Perhaps you could even use Ammonium Chromate or DiChromate. Another possibility is that it is not the chromium ion that makes the difference; just that Potassium Dichromate is a strong oxidizer. That possibility would be easy to test by using another unrelated oxidizer like Potassium Permanganate.

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