Rapid Set UltraFlow is a precise, fluid, non-shrink grout. Rapid Set UltraFlow 4000/8 offers you advantages that no other grout can match. A fluid-consistency grout, UltraFlow 4000/8 gives you extended working time in large placements. It gains strength quickly after 1 hour and reaches 4,000 psi in 8 hours. In the past, you may have had to choose between long working time and early strength gain, but UltraFlow 4000/8 provides both of these qualities. Pumpable and easy to place, UltraFlow 4000/8 doesnât bleed or use gas-forming agents so no hollow spots form under the plate. Complete jobs faster by removing forms and completing cutbacks sooner. Paint or coat UltraFlow 4000/8 in 24 hours. One 55-pound bag yields 0.5 cubic feet.