Irregulariteit of less than 2 mm can be levelled easily using an appropriate underlay. However, it is always important, to determine the nature of these imperfections. Bridging grooves from an existing tile floor, for instance, requires a hard underlay of at least 5 mm in thickness.
Small imperfections—like sand, concrete grid or glue residue—confined to limited areas in your base floor, call for a softer underlay. The soft material will easily incorporate these tiny bumps and holes and create a smooth flooring surface.