UE 4.19 APEX Destruction. There isnt a second Material for Chunks

i have a simular problem…my mesh is closed…it creates faces where the mesh is cut…but it only has the original material slot…and i don’t get another slot for the inner parts…so it just tiles the original material over and over on the cut faces and looks really bad…i tried to add another material but doesn’t work…any idea what is wrong?