A friend of mine has a juniperus bonsai similar to [this][1], but it is not doing well recently.

I noticed its top roots are now outside of soil, which I find not good, and I am about to suggest my friend adding a thin layer of a good substrate to cover exposed roots. But I am not a bonsai expert, so I am asking you - am I right?

Update: Photos:

[![enter image description here][2]][2]

[![enter image description here][3]][3]

[![enter image description here][4]][4]

[![enter image description here][5]][5]

[![enter image description here][6]][6]


  [1]: https://imgdbg-dallasbonsaigard.netdna-ssl.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/p/h/photo_sep_02__8_01_36_pm.jpg
  [2]: https://i.sstatic.net/9k9Sl.jpg
  [3]: https://i.sstatic.net/xdi9M.jpg
  [4]: https://i.sstatic.net/tQL2Q.jpg
  [5]: https://i.sstatic.net/v7G8C.jpg
  [6]: https://i.sstatic.net/xR3I3.jpg