recently I built a step out of concrete (quikrete brand) between two other concrete pads in my back yard. Intent is to have a base that I can tile over. The concrete has cured for about a month or so and I am ready to tile. The top surface of the step seems to be disintegrating -- the more I sweep or brush the surface the more of the step I remove. The sides of the step that were covered by the forms are rock solid and appear to be ok. Since I am tiling over the step I am not worried about the appearance, but I would like to stop the cement from "shedding" before I try to cover it. I have tried brooms and steel brushes but cannot seem to remove enough of the top to read a firm surface. My next step seems to be to get a high power pressure washer. Any other thoughts of what I should try ? I have though of trying a sealer but I am worried about adhesion with the thin-set mortar.
I have done several concrete project and this is the first time this has happened -- not quite sure about the cause.