Clearing grid with 2 dices

A user throws 2 numbered 6-side dices. The combination that comes up is coordinates into 6x6 grid and that cell gets eliminated. The same combinations might happen multiple times, so if the cell was already eliminated, the throw was useless. I would like to see how many steps on average it will take to clear 10% of the grid, 20%, ...,  90%, 100% of the grid