It is better to grind it or get the Fine-grade. It is available (Many places don't stock it though).

If you wish to, you may grind the Celtic in a mortar/pestle or a blender though..

NEVER use a 'Pepper Grinder' for the 'moist' looking sun-dried Sea Salt s, like Celtic, because the mechanism will most likely rust, especially if left for long periods. There are specially made Salt Grinders. Look for the the grinders with a 'ceramic mechanism', they come in a range of prices much like Pepper Grinders.

and both works fine for me, but I thought that celtic salt has more cleansing effect on me though..