2 - For the unwrap I have used UVLayout, rendered the unwrap object image and again it was saved as an *.obj
3 - The object was imported to ZBrush and with a few subdivision levels I've started to create details like the stones in the wall, wholes and much more. With the finished details I've turned the object to the lowest subdivision level and again exported that and also exported (Flipped vertically) the created Displacement
Map (Ref. ZBrush).
4 - Finally in max I've replaced the old wall object by the new one and now I had it unwrapped and with a Displacement Map and an image rendered in UVLayout showing all the edges to guide me for the texturing process.
UV Mapping -
After the modeling, organized objects in scene and the final camera decided I override all materials with a middle gray. I've created a sun light and decided it's direction and it's color. Since I have in mind to create a sunny day I gave it a nice strong warm color intensity and make a initial lighting setup (for this scene I've used V-Ray).
This first lighting step helps to create the scene textures without making drastic changes in the materials output and preserve the original colors I've created in Photoshop. I've used Gamma Correction (2,2) in the Max Preference Settings.
Next step, for the Unwrap I've used UVLayout, it makes it very easy and perfect. To do that I've exported individual objects in *.obj format and imported then in UVLayout. For this process you can find nice Video Tutorials in the UVLayout website (http://www.uvlayout.com).
Then they are imported again into 3ds max, replacing the old objects and renamed again.
Texturing -
With the rendered image in UVLayout of the unwrapped object, now I have opened them in Photoshop and I got the right directions where to fit the textures in the object, as all the object edges are visible in this render.
Now I went to my rust texture library searching for textures that could help to create the perfect final texture for my scene models. In this process I've used several textures using blending modes in Photoshop adjusting Brights and Contrasts, Hue and Saturations, Levels and so on, painting and blending the different texture layers
(Usually Overlay)
