Ban facebook in office?

There is no need to ban facebook. Employees are not child. They should know what they meant to do in the office and as long as they keep you happy with their performance, you don't have to worry about it. Giving them freedom to use facebook will make them work harder in the remaining time. Restricting them will not do you any good as it's up to them how fast/slow they want to work. Also you will lose some respect that way. Everyone got smartphone with wifi nowadays anyway. So you can't win.

Try playing some fun games in facebook with them in lunch hour.lol. A friendlier boss is the most respected one.

I think an employee who wants to muck about during office hours is going to muck about during office hours - block Facebook, they'll either use a workaround or find a non-Facebook way of mucking about. Block the whole internet if you like, they'll still be writing blogposts and fan-fic in Word, remove their computer and I bet you they'll develop a sudden interest in reading industry-relevant magazines, or "negotiating" and "improving relationships" with supplier reps... there's always a way of killing some time for a person who wants to avoid their specific work tasks. Or indeed for a person who isn't sure what he/she should be doing and doesn't have the confidence to just start tinkering, or to interrupt the Very Busy Boss and ask what comes next.

I don't believe it's related to pay grade, and permitting or restricting internet access based on salary rather than on job role is just going to insult the lower-paid employees. I think it's more related to whether someone reckons they can get away with it.