3M WETORDAY SANDPAPER Use wet or dry for sanding old finishes, fine featheredging plus surface work. It is a silicon carbide, closed coat product bonded with a waterproof resin. Versatile sheet can be used wet or dry on paint, primer, gel coat, metal, and wood finishes. Waterproof backing supports wet applications for decreased loading and a faster cut. Strong C-weight paper backing provides durability for either hand or machine sanding. Sold by each.