Prepping Concrete on a Large Patio?

i have never used one to prep concrete myself but tried to paint concrete patio for a friend last year.after sanding it down and primering it let it dry for a couple days as we were fighting alot of rain last spring we got to paint it. well with in a week it didnt look so good anymore, all the moisture in the concrete made the paint bubble up something fierce! she called another friend of ours as i was busy working and they rented a floor sander to get all the old paint and primer off. of course this left allot of hand work around the edges but she took care of it with a hand held sander and some 40 grit paper. when the got it done they put ceramic tile over it! it looks great but was expensive to tile . just an idea for you to look into is all. good luck and remember, have fun while doing it and you will enjoy it more later!