Are professors really responsible for labs? I think the right persons to confront are the lab technicians. Anyway, the thing here is, if you have to email them, then make it official, start with "Hello" then go straight to the point.No need of going through shortcuts.
After a period of time and they don't reply, then go straight to the location and ask whether they'll accept you. Actually, it is going to present yourself to the institution rather than sending emails.