The most beautiful and the most conditional
Cutting past the sand into the stone turns a slab into something that looks like terrazzo and costs a fraction of it, and on the right floor it is the best-looking thing we do. It is also the one finish where the answer might be no. The stone has to be evenly distributed through the pour, the slab has to be flat enough that a consistent depth of cut is achievable, and there has to be enough cover over the reinforcement to take the material off safely. Those are properties of a pour made months or decades ago, not decisions available now.
Why we test-grind first
A test grind is a square metre taken to full exposure in an area that will be covered or is out of sight. It takes an hour and it answers every question: what stone is in this mix, how evenly is it distributed, how deep do we have to go, what will it actually look like. We do not quote a full aggregate polish without one, because the alternative is quoting a finish that the slab may not contain, and finding out halfway across the room is not a recoverable situation.
Specifying it in a new pour
If a slab is being poured now with a full aggregate polish in mind, the decisions are made at the concrete order rather than at the polishing stage: aggregate size and colour, mix design, placement, and a flatness specification the finisher is held to. A slab placed to be polished costs slightly more and produces a dramatically better floor. It is worth involving whoever will polish it before the concrete is ordered rather than after it has cured.