Plastering a wall is incredibly hard to do without extensive practice. Having done some plaster, but only on interior walls (not drywall, real plaster), and some finish concrete and masonry work. Pool plaster is the final coating applied to the shell of a concrete in-ground pool. The layer of plaster is normally 1/4 inch to 1/2 inch thick. White is most common, but it can be tinted to other colors by using pigmented aggregate. Many folks re-plaster the pool during renovation, about every 20 years or so. Some do it more often to keep a nicer finish, or to change colors.