One object, lots of materials I made a stone cabin in blender but I forgot to set materials to different parts of it and I joined it all together.

Is there a way to set materials to loose parts or do I have to separate it (which would give me about 300 loose parts)?

If there isn't, can I somehow separate loose parts one by one (so that I can separate for example all parts of roof and rejoin them separately)?
You can separate mesh in editmode with P. You get some options to choose, I think they are self-explanatory:



To select specific loose part select any of its vertices and hit Ctrl+L.

You can also add multiple materials to object and each apply to specific faces:



Make selection and in edit-mode hit Assign. The first material slot will be the default one.