Limit UV

This is something that has been bothering me for some time. It’s probably quite simple really. How would I unwrap certain faces of an object? I once made this wall with some 30 faces on it. All I did was select certain faces, unwrapped it, and there they were in the UV Image editor. ONLY those faces. From there I toyed with it and used alpha mapping to make blood stains on the wall. Now, I’m making one of those floor signs (Wet Floor) and go to unwrap certain faces but the whole object gets unwrapped making it a little difficult. One person said that I just need to move the unwanted faces off to the side and leave only the faces I want inside the bounds of the image. Another person said that i need to add another UV layer for the selected faces. My main question is…How was I able to unwrap only the selected faces with my wall but when it came time to unwrap the floor sign the whole object got unwrapped?

As soon as you create any UVs, ALL faces will have UVs assigned to them automatically (by default each face is assigned the full UV space). You cannot have some faces having UVs and some faces not.

You can move faces outside the UV space and prevent any texture from tiling with either a mapping node (cycles renderer) or using the Clip option in the Image Mapping panel (blender internal renderer)

Are there consequences to making only the faces I want changed into a different object using seperate then joining everything back together? Come to think of it I think that’s what I did with the wall and blood stains. It seems like this method gives me better control over the uv’s…but this may do more harm then good in the long run.