Most would not think that you can polish concrete as it seems to be such a matte surface with no chance of taking a shine.
And that can be true if the concrete is too soft or constantly "dusts" which means the surface is soft enough and loosely bound enough to be wiped away.
Some concretes could never be polished if it were not for concrete hardeners, these products flow down into the concrete and capillaries of the Concrete and then grow crystals and react with the lime in the concrete. Generally hardeners or densifier as some call them will not penetrate as much as water because of the solids present in the hardener. To the degree that they do penetrate they do harden the surface and help bind the grains and particles together.
This is what allows the concrete to take on a shine; even so concrete will only hold a shine of 1500-1800 grit polishing pads even with the hardener present.
Shines higher then this require a polish or acrylic product used with a buffing machine to really pop a shine, this does defeat the purpose of polished concrete, which is to have a low maintenance floor. Use of any polishing agent or coating will hold dust, peel off and or dull with time requiring more maintenance.
Concrete on it's own with a hardener is a perfectly good shine and can be about as shiny as a store bought marble tile.
This level of shine is quite adequate for a number of requirements from Warehouses, Retail Stores, Discount stores, work shops, and high end homes; it really does depend on how good a pour the concrete was, as to how nice a polished floor will be.
Some contractors will let the concrete sub know that the floor will be polished after the pour and therefore more care needs to be taken with the quality of the concrete, how likely it will be to crack, have dirt, twigs or voids in it, or even if it will be trowel by hand, machine or not at all. (More on this)
The concrete will need to be opened up with a low grit Metal bond grinding pads to prepare it for the hardener and to generally level the concrete along with removal
of trowel marks if any. Just which low grit to start with, takes experience, but in principle the smoother and more level the original surface the higher the grit that you would start with. Most floors are started with a 30 grit diamond pad and these are available in different metal bond hardness’s.
Polishing steps are usually double the last step so after a 30 grit the next step is a 60 or 70 Grit and then a 120 grit and so on until it is time to switch to resin bond polishing pads.
Most contractors switch over to resins at about 120 -150 grit metals.
It is not recommended to go beyond 300 grit in Metal bonds as it leaves fine metal fillings in the concrete which makes the concrete look dirty or blotchy.
Using metal bond tooling up to 200 grit or 300 grit does reduce “ponding” which is the ripple that you see on the surface of a pond in a still photograph of a pond.
Ponding becomes apparent once the floor starts to shine, before that it is too slight an effect to measure or see by any means.
After switching to the resin bond diamond tools the same process is followed of doubling the grit until the shine desired is achieved.