Simple and Inexpensive Faux Concrete Wall Finish 

After searching all over the internet for a way to create a concrete wall look, we settled on using Feather Finish, which is an easy to find and inexpensive product. With that, and a trowel, we refurbed an accent wall in our bathroom in just a few hours, and were thrilled with the result.
This is the product we used, probably also available at your local lumber / hardware store:
W.W. Henry Company Feather Finish Coat, 7 lb
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