Per the product page
2 - Do I have to use Eraser between Essence and CQuartz?
If your using Essence by machine and you wait until the vehicle is finished then you can apply Reload or CQuartz after you finish the vehicle starting in the same direction you polished. If you want to be ultra safe you can still Eraser but in our testings to date we have not seen any failure when we skipped Eraser.
If your using Essence by hand then we recommend you use Eraser before coating.
5 - How does it work if you use it between the paint and CQuartz?
It bonds to the paint, the CQuartz bonds to it and merges. The SiO2/resin in it are heat activated by the machine polishing process. If using by hand or in very cold temps you should Eraser the vehicle before coating.
With that said I still wipe down the surface after letting Essence sit for a few hours after initial wipe off.