These Wet & Dry Sandpaper Rolls have a strong flexible waterproof backing making them ideal for wet or dry sanding of painted metal, aluminium, brass, plastic, finished concrete and dry walls. Can be used by hand, with a block or on a clip fixing machine. Wet sanding is typically done after dry sanding to get an even finish. Unlike dry sanding, wet sanding is done not to shape a surface, but to remove the large scratches left by dry sanding. When done correctly, the surface will be slowly levelled out, and the scratches left behind will become smaller and smaller, until the light they reflect no longer makes them visible. The grit of a sandpaper refers to the size of the abrasive particles bonded to the paper. The higher the grit, the smaller the particles, and the finer the scratches left behind.