I try to do a wall with multiple layers (for example, a wall with a layer of a damaged concrete on top of base of bricks, and we can tee the brick when the concrete is damaged.)
The wall is in my foreground, so I need an enough good way to have sens of volume on the concrete layer.
I have tried multiple techniques (using multiple objects with alpha or displacement, or one object with shader mixing my two texture) but nothing seems satisfactory.
Is there a good way to do that?
Your question has multiple solutions, but I would solve it in a material, not via modellling.
In theory, you can simply do it procedurally with the two materials, a mask for the damaged areas, and then mix them.
If you want more realism and less tweaking, you can do exactly the same with PBR maps.
Displacement is optional but may help your cause
Would you like me to try and upload something this evening?