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Picture of Making blackboards on concrete walls
I decided that since the girlfriend NEVER makes lists, unless I stand over her and insist she make one for me, that I  would put one smack next to the door leading out of the house.  My son is provided to give you a sense of scale.  And show why I made it as high off the floor as I did.

Step 1: Proper Prep work makes the project (the seven P's are Proper Prior Planning Prevents...)

This  part is pretty easy.

Figure out where you want the  blackboard.
Sand/ scraper it smooth(ish).  There is no need to get all Rainman obsessive about this part.
Tape off the borders.
Buy a can of blackboard paint.  And a brush/ roller as needed.  You CAN make your own paint, but it's SOOOO cheap; why bother?

Could have SWORN I took some pictures of this step, but apparently not.

If you need a detailed explanation, with pictures, for these steps, send me $99 and a Stamped, Self Addressed Envelops (SASE) and I'll make you your own little Instructable...  Or alternately, you could  just ask ANYONE  that has the first clue.
 

How fun! Blackboards and the best for drawing on in my opinion :)