Thanks xendance for the info. I will use this technic for my walls details, but i'll keep using my 90 degrees corner plane for this purpose because i have an arch to do as well and I cannot apply a decal material for this.
I use a detail Normal map for my walls. For the base color I simply use a constant 3 vector and i added a custom mask i did in photoshop. I also added decals here and there for those cracks and specific details.
I wish Japanese developers were more open about showing off their assets and talking about how they create stuff, like western devs do. Would be a lot easier figuring things like this out. Although it seems easily explained now through UE4 decals.
I tried to find some info about making decals with normals map only wihout albedo or anything else and it seems to be impossible, so it's basically a 90 degrees corner plane with the same details normals map apply to it as the walls with a second normals map with grunges that i did in zbrush. Very subtle but this is what…