Chemical sealants are usually added after the initial sanding because this will further harden the concrete. When a chemical sealant is added to concrete, it penetrates deeply into the concrete and creates a chemical reaction that produces a byproduct that fills all the pores in the concrete. This hardens the concrete surface and also reduces pit formation.
During the curing polished concrete process, the concrete slabs produce a by-product called free lime. It is calcium carbonate and when it reacts with concrete sealants it produces the product which is a hydrated calcium silicate gel.
These are very hard and dense crystals that form a continuous layer. The chemical reaction binds the concrete and sealants, making the plates tougher than ever. Of course, it is also possible to add solid aggregate to the concrete during pouring, which gradually opens up during polishing.
There are three grades, and Grade I is known as cream coating, which does not expose any aggregates when grinding to a very even tone.
Grade II is "salt and pepper" and results in partial exposure to the aggregate. Grade III is the finish and exposes more of a filler, resulting in a terrazzo-like finish.
If the soil is likely to be exposed to oil, grease, water, or even acids, i.e. In commercial kitchens, a final sealant layer can be added to the floor, which significantly increases the resistance of the floor to it.