I encounter this problem on some models. The material does not apply to all object polygons. When merging (Ctrl+J) this object with another, the "unregistered" polygons will be assigned to the other material. Why does this happen and how can it be avoided?

I can manually assign the material to all the polygons in the model, but i don’t understand why it wasn’t assigned initially if there are no other materials here. I didn't have a problem with this during the texturing phase, but it only comes up when I need to merge meshes.

material selection enter image description here

  • $\begingroup$ If you join an object with no material with another one that has several materials, the first one will inherit the first material of the second one, if this is your question? $\endgroup$
    – moonboots
    Feb 19 at 15:32
  • 1
    $\begingroup$ No, the first object has the 1st material, and the second object has the 2nd material. But Blender thinks that the first object has polygons that are not registered as the 1st material. My question is how is this possible if the first object has no other materials and all its polygons display the same material in the viewport? At what stage could this happen, if even when texturing in Substance Painter I did not have any problems with these polygons. $\endgroup$
    – solo_GRV
    Feb 19 at 15:39
  • $\begingroup$ This is indeed weird to me, if an object has only one material assigned all its polygons should point to it. I think it is possible to circumvent this rule if you somehow create the mesh programmatically or if it comes from another software. How did you create this mesh ? $\endgroup$
    – Gorgious
    Feb 19 at 15:50
  • $\begingroup$ if you had added @moonboots then he'd be notified of your response, unless he's following the question $\endgroup$
    – james_t
    Feb 19 at 15:50
  • $\begingroup$ can you add a screenshot of before/after UVMaps that could be some clue? Or perhaps a reduced-detail version of you blend file so others can analyze? $\endgroup$
    – james_t
    Feb 19 at 15:52


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