Of course, there is some routine admin work that does not demand cloistered seclusion, and most teachers are happy to multi-task to the extent that they can cope with a cup of tea and a conversation while this work is being carried out. In this case, you should not object to being interrupted, but should be prepared to stop what you are doing briefly if a colleague has a work-related issue they need to share.
However, you should apply the same kind of ruthless prioritisation to interruptions as you do to e-mails. If a topic is going to take more than a couple of minutes, you should arrange a time to discuss it later.
If you are sitting in the staff-room doing routine work, then you're fair game for interruptions.
The situation needs to be different if you are doing important work (note: 'important work' includes anything relating to planning and assessment) and you need to take the initiative in making the situation different. Take yourself, and your work, somewhere where interruptions are difficult. You should tell someone where you are going, but also tell them that you don't want to be interrupted.
If possible (this is not always possible in school) set up your workspace in a way that discourages interruptions. Only one chair - yours. Door: closed. Doesn't work? Try a 'Do not disturb' notice outside.
If you are interrupted, handle it politely but firmly; ask 'How can I help you?' but unless the topic is both urgent and important, you should arrange to discuss it at another time.
There are several popular interpersonal tactics to discourage chatty colleagues, like standing up when they start a conversation, or avoiding eye-contact when replying, but these tend to work in some contexts and not in others. It is much better to simply be assertive and tell colleagues if you need to be undisturbed.