Exposed inner surface area of wall

[shershahbacha9]

i need to apply material to inner surface of wall by paint so that i get the area in Material take off schedule. But i need to apply material to exposed inner surface of wall and not in wall joints. I mean if i select a wall and apply paint , the paint is also applied in the joint as its a part of wall (As seen in picture 1 ).

I can do it by splitting wall face everytime but is there anyother method? I tried by join geometery for two walls joining but could not. Is there any method for creating these walls so that when i wanna paint the inner surface of walls, only exposed area is painted and not in joints. I need the area for tiles on wall. All i want is in this pic 2.

[ennujozlagam]

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