Character; why does Peter Wilmot seal off rooms in people's houses?

Peter Wilmot is a main character in the novel, Diary, by Chuck Palahniuk. Before he fell into a coma (which he has been in since the beginning of the book), he would seal off rooms of people's summer houses and write obscenities inside of these sealed off rooms. At this point in the book, the reader is still not quite sure why he does this, or if there is a reasoning behind what he is writing on these walls. One could speculate that he is either going mad, or he's got some kind of agenda to follow that is obligating him to write these evil obscenities on unsuspecting people's walls.
I've been reading this book on a kindle, so the pages are all wonky, so forgive me for that now.
There is a quote that relates to this topic on page 347; "Every contractor, Misty tells him, they'll sign their work. Mark their territory. [...] They'll write on the walls before the wallpaper or tile. This is what's inside everybody's walls, this record of pictures, prayers, names. Dates. A time capsule." This might have something to do with why Peter was writing on the walls of the rooms he sealed off. At this point, though, it's still up in the air, and with an author like Chuck, there's no telling what could happen.