Like the crumbling plaster brick wall, the signs of rot and damage are used to describe the age and history of our set. The Set Designer becomes the Architect of the rot. Their job is to design a believable set. Which walls are rotten or burned. Where the rot or fire etc. came from.
By illustrating the elevations, a Scenic Painter knows where to place the elements. Where the rot is located in the walls tells the audience about the building the set is in. Often the set being built is just a room. (A room in a bigger building. Or a single space.)
To ask a Scenic to place the aging elements based on a photo reference is a gamble. Although they are excellent at re-creating the look of the destruction, they often don't know the context of the room they are aging, nor do they all think about where the damage would come from in the building, or what the building exterior is made of. It is such an important step to add the scenic detail in decrepit elevations. Even just by Sharpie. It can so easily go so wrong. Its a really common oversight.
We don't go to school to learn how to destroy things. Architects and
Draftspersons are trained to design structures that are meant to
withstand the elements. Set Design often calls for decrepit. A Draftsperson coming into film from an Architectural or
Engineering firm has been taught that they could be fired for adding
illustrative elements to a drawing. Then they find they can become key players in designing destruction if they are in any way artistically inclined. They know "rot theory" and are good at it. Seek them out.
Its a complete reversal of what we have learned in school when we come to the Art Department.