I am trying to make a wall texture that has a tiling bump map for the texture of the wall, and a UV mapped bump map just at the bottom of the wall for the baseboard. I layered the wall bump map first, then the color for the baseboard, then the bump map for the baseboard. When the wall bump map is mapped to color and not normal, the effect is what I want: that the baseboard overrides it. But when the wall bump map is mapped to normal, the two bump maps mix together.
So why is it that textures mapped to color can be stacked up and the effect is that the bottom, most recently added texture overrides the previous ones in the areas where they coincide… but that textures mapped to normal only seem to mix together?