problem with concrete

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.
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On Sun, 25 Sep 2005 22:22:49 -0400, "Sam the Cat"

You are describing classic "spalling", usually caused by concrete that dried out before it cured. That is common in the summer if you don't cover it and keep it wet.
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No I did not -- so what's the cure ? Anything I can do ?
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Not sure why you would be tiling a concrete step, but you will need something like thinset to lay the tile into. That should fix the problem, until a frost peels off the tile anyway if you get any cold weather at all.
AMUN
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On Mon, 26 Sep 2005 19:01:47 -0400, "Sam the Cat"

***** START OVER *****
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