How to write to employees to be on their desk and chit chat in office place

Hi all,
I have recently joined a firm, it has around 30 employeses there. The company don't have much work load and most of the time people are free. In that situation usally sit with other colleagues at their place instead of their own.
Can someone please hekp how can I write to staff that they should not hang aroung and chit chatting for hours in office in a proper manner. So tha I can keep discipline at workplace.
Thanks

Unless and until you find sufficient wok load, this kind of moving around will take place.Circulars can be sent but effect will be minimal.
Is the company having excess employees or it is a temporary phenomena where company will expand.