Sanding is very good at removing defects at wood surfaces, but it creates a surface that contains minute scratches in the form of microscopic valleys and ridges, and also slivers of wood cell wall material that are attached to the underlying wood. These sanding ridges and slivers of wood swell and spring-up, respectively, when sanded wood is finished with water-based finishes, creating a rough fuzzy surface. This defect is known as grain raising. It can be eliminated by wetting the surface with water, leaving the wood to dry and then lightly sanding the wood to remove the ‘raised grain’.