Why can't I scale the mesh? I have 2 meshes and I added a 3mm solidify modifier to both of them. The upper red mesh looks merged to me, so I want to scale it a little so that I can't see the red mesh from black. 

In the edit mode I select all the meshes and press Alt+s to scale it a little. It's going up or down, but I can't scale little to make it smaller. I applied scale and rotation to both yet to same result. Does anyone have any suggestions or help on how to make it work?
From what I understand try just pressing s + x/z/y instead of alt s. Also make sure proportional editing is off