Look for holes or cracks in the floating slab that you want to waterproof. If you see any holes or cracks in the floor, brush them out with a wire brush to remove loose particles, and fill the holes or cracks in with leveling compound. After a few hours, when the compound dries, feel the areas that you filled to make sure they are even with the rest of the floor. Chances are, the filler won't be exactly flat and you'll want to sand them down with medium-grit sandpaper.
Clean the surface of the floating slab with soapy water. Use a cleaning brush and scrub any caked-on dirt or greasy spots until the surface is clear. Once the dirt and grease have been removed from the floor, use a wet mop to remove the soap from the floor's surface. Rinse the mop every few feet to make sure you aren't just spreading the dirt around.
Put plastic sheeting down along the bottoms of the walls, taping the sheeting down at the very bottom of each wall where it touches the floating slab. Cover any fixtures that sit on the floor, such as hot water heaters or pump, with plastic sheeting.
Wear a respirator mask and pour waterproof concrete sealer into a paint tray. Starting at the wall farthest from the door or entrance to the basement, begin applying the sealer at the bottom of the wall with a paintbrush. James Dulley recommends using a circular motion when applying sealer with a brush to work the mixture into all the walls crevices. Apply the sealer to the bottom 5 to 6 inches of the wall, and then continue applying the sealer at the side edges of the walls and the tops of the walls by the ceiling. You are "cutting in" the edges of the wall, which won't be reached by a roller.
Finish sealing the wall by applying the sealer in the center section of the wall with a paint roller. Place the roller down at the edge of the sealer you applied with the paintbrush, roll the roller back into the sealer that is already applied, and then roll forward a few inches. Apply sealer to the other walls in the basement in the same manner as the first wall.
Begin applying sealer to the floating slab floor in the corner of the room farthest from the door. Just as you did with the walls, apply sealer to the edges and corners of the floating slab with a paintbrush. Work your way down the adjacent walls from the corner with the paintbrush until you have a perimeter of 5 to 6 inches of sealer on all sides of the floating slab.
Apply waterproof sealer over the rest of the floating slab with a paint roller on an extension pole. Begin at the farthest wall from the door and work your way out of the room.
Use this process to complete the application on the entire slab. Wet the roller with sealer, place the roller against the floor at the end of the most recently applied section and roll backward into the area where the sealer has already been spread before you roll forward. This helps eliminate streaks on the surface of the floor.
Allow the sealer to dry for eight to 10 hours. Apply a second coat of sealer. If you want a third coat of sealer for extra waterproofing, again wait eight to 10 hours before applying the third coat to the floor.