This is going to be a very noob question. I am probably missing a concept.
So I have a room, created by very thin boxes:
I play changing the materials that are already provided by the engine, all ok. Then I try to model(blender) a ship-like door, export the mdl file and the materials are not showing as expected. As you can see the front wall is full grey while the materials in side walls are correctly showing the stone material. I have to point that some of the faces of the object looks to render the material.
In my research I understood that I would need to take care of the UV mapping and the normals of the faces, which I think I did:
What else am I also missing?