It compacts well because of the varied sizes. When you apply the vibrating plate or use a hand tamping device, the little stuff is shaken into the voids between the larger stuff.

So "Class 2 Base Rock" is the correct product to use for the base of a small paver patio?

It’s also location specific. Rock is heavy and expensive to transport. What is available in one location may not be available in another.

@Sophie the term "Class 2 Base Rock" appears to be widely used across the US and appears to mean either crushed limestone or recycled concrete, 3/4" on the high end and includes all the fines on the low end. If you search that term on Google you will see that a wide variety of rockeries advertise that product.

What is less clear is what is the distribution in the mix of different sizes. Some products I see online appear to be mostly large sizes and very little fines. It's hard for me to understand how that could ever compact to a flat surface.

I’m aware of what it is and how it is used. It’s also not available in many areas of the country due to mining and shipping issues. Which is why I recommended that you find out what is available locally.

@sophie what is available locally is "Class 2 Base Rock"

@Matthew thank you for that confirmation. The 411 product in Ohio appears to be crushed limestone and includes and lot more fines. Our product is recycled concrete, so there is a lot less breakdown into fines. I'll just hope for the best.

I defer to YouTube

If you view any of the 30+ videos on Youtube for building driveway, paver, and similar-application bases, there is not a single one where they do not care about making the sub-base smooth, flat and level. There is a target grade, and they spend a LOT of time to make sure the sub-base is level to that grade and has an extremely dense and flat (and visually smooth) compaction.

The purpose of sand in a paver install is not to level the pavers! The purpose of sand is to fill the gaps between the pavers, on their underside, and thereby lock them into place. Of course, you do approximately level the sand layer, but you don't compact it because you want the sand to slip up between the pavers. The additional layer of polymeric sand applied on top of the pavers does the same thing on the top side.

Further proof of that point is that in installations where there is a large space between stepping stones, they typically install the stones directly on the compacted sub-base without sand. They fill the gaps between the stones with mortar, polymeric sand, or dirt (depending on application). In that application, the sand over the base layer would not fill the gaps between the stones, so it is not needed.