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.
Did you cover it with plastic and keep it wet ?
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.
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.
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