White fuzz or powder appears on the concrete surface

Q. Why would a "white fuzz", I am assuming its a mold, grow on my concrete floor in my shop, in any area, after water has been on it and dried?

A. This "white fuzz" you are referring to is called efflorescence. Here's what is happening, water on the surface of the concrete gets absorbed into the concrete. As the water dries, it escapes back up through the concrete's pore structure as vapor carrying with it minerals and salts from the concrete. These minerals and salts get deposited on the surface of the concrete after the moisture vapor evaporates and leaves behind this white powdery looking substance.

You can read more about this common problem at how to remove concrete efflorescence.