Why does ice stick to a cement block wall?

My kids were playing outside the other morning, supposedly watching a piece of ice melt.  Incidentally, the ice contained the popcorn mentioned in my previous post.  Ever since watching the Sid the Science Kid episode with fruit frozen in ice, they have wanted to freeze everything!

Anyway, my son ran back into the house shouting, "Mom, come quick!"  Slightly worried that my daughter might be lying in the yard injured, I hurried outside to find this.

The ice was sticking to the wall!  Of course the next question from my kid scientist was, "Mom, why does ice stick to walls?"  

 You may be surprised, but I do not remember that being covered in any of my classes.  Maybe at the master's level?  To be honest, the fact that ice sticks to cement block walls had eluded me until just then.

So, here is a question that I would love to have a good answer for.  Why does ice stick to a cement block wall?  I would guess the temperature was 70 ish F, or 20 ish C.  The ice was fairly flat, and eventually did slide down the wall.  The wall was slightly damp and covered in side walk chalk.  I have several guesses, but nothing authoritative.  Thoughts?

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