I recently came across the phrase "一面墙" in a novel. Does this phrase usually just refer to one side of the wall? Or is 面 a general measure word, referring to the whole wall (and not necessarily just one side of it)?
Without more context, I'd take it to be in reference to a wall that has one side (that is visible from the speaker's perspective). Strangely, 这面墙 or 那面墙 can refer to one particular side of a multi-sided wall to me.
Edit: Thinking about this again, it'd really depend on the context. This is what 一面墙 conjures up in my mind at first:
粉刷一面牆得花兩千塊左右==> I would naturally assume it is a two-dimensional concept referring to only one side of a wall.
通道盡頭不知何時砌了一面牆, 堵住了出口 ==> Of course, it is a three-dimensional wall (i.e., the whole wall) blocking the exit. However, the speaker uses "一面牆" to imply that (1) you can only see one side of it (i.e., unable to see the other side) from the 通道, and (2) the surface of the wall is relatively flat or smooth, assumably plastered.