Fig.14 shows the far wall using a more conventional texture that composes of a single JPEG which has been manually put together in Photoshop using a number of source images. It uses a Standard material with a single color map assigned to the Diffuse slot (inset).
You can see in Fig.15 how at least six different textures have been combined to create this texture.
The same technique has been used for the door, which incorporates three textures from Total Textures V17 - Urban Extras Textures.
Total Textures V7:R2 Urban Textures
Door_09 has been set to Darker Color within Photoshop in order to reveal just the rusted areas and the graffiti from door_13 has been extracted and then set to Overlay on a separate layer (Fig.16).
In the case of the right hand wall, both of the above techniques have been used, i.e. an unwrapped template used as part of a composite layer.
In Fig.17, the mask from Layer 2 (tile02medium_13 V05:R2 - Dirt & Graffiti is visible in the scene which is creating a stain using the opposite texture (1).
Total Textures V5:R2 Dirt & Graffiti
The base layer however is a custom texture made in the same way as in Fig.15 & Fig.16 and has been created over a wireframe guide that represents the unwrapped wall (Fig.18).
The red arrow indicates the two sections of wall to the right and the lower section corresponds with the two panels at the opposite end (green arrow). The black "L" shape has been left incomplete as this section of wall falls outside of the camera view. The two horizontal lines towards the top of the wall represent the grime and shadow from the two larger pipes.
The final scene can be seen in Fig.19, which is built up from both composite maps and custom textures created in Photoshop.
To see more by Richard Tilbury, check out Digital Painting Techniques: Volume 4
Digital Painting Techniques: Volume 5
Digital Painting Techniques: Volume 7
Beginner's Guide to Digital Painting in Photoshop Elements
Beginner's Guide to Digital Painting in Photoshop
Photoshop for 3D Artists
and Prime - The Definitive Digital Art Collection