Don't use absorptive materials on any surface in restrooms. Kids don't use a bathroom and leave. Water fights break out. Toilet paper gets wet and thrown at the ceiling. Toilets get deliberately clogged and overflow.
Absorptive materials absorb odors and waste as well as water.
Plaster, concrete, dry wall, acoustic tile and wood are highly unsanitary materials to use in restrooms. 2.Ceramic tile, glazed concrete tile, or properly sealed terrazzo are good alternatives to absorptive materials. If you do use terrazzo and ceramic tile, bring the terrazzo up to form a three-inch base along the perimeter of the bathroom. That will eliminate water and waste collecting along the wall. Don't install exterior insulated pipe where workers or children will damage it.