I want to install a ceiling fan below an old plaster-and-lathe ceiling. I was thinking of running a piece of wood between two joists in the attic above, then screwing a pancake electrical box directly into that piece of wood.
Rather than cutting into the plaster, I'd simply install the box on the surface of the ceiling (and screw through it to attach the box to the wood above). In other words, the box would not be recessed into the ceiling.
My reason for wanting to do this is that the ceiling is old and not in excellent shape. I worry that if I start cutting into plaster and cutting up lathe between joists, I'll invite more plaster cracks. I'd rather leave the plaster untouched.
I know that you might be able to see the box slightly with this installation method (although I am hopeful that if I get a small enough box and a fan with enough play in the part that covers the box, I can hide everything). I'm not too worried about that, as it should not be very noticeable -- certainly not as noticeable as more cracks in the ceiling.
Are there any other reasons why I couldn't do this?