We washed some newer concrete---9 months old, and a grey silty grit seemed to wash off the surface. Also, when washing no matter how many times we passed over the surface there were many overlap marks and just an overall very inconsistant look. It seems to be something to do with the concrete being soft(all the silt washing from the surface) but this has only happened maybe one other time and I wanted to see how common this is, and see if there are any fixes. Thanks
Also - we did use a surface cleaner
Also - we did use a surface cleaner