Stripping is a process when you get rid of everything on your surfaces using chemicals, following by mechanical scrubbing, or pressure washing. Most of the time we use pretty strong chemicals, which could be harmful for our health, but if diluted and properly neutralized they safe for people and animals around.
Most people think of deck refinishing as simply pressure washing. But there’s no way to get rid of old stain with just a pressurized water. You must first dissolve the old finish, dirt, and mold on the wood surface. If you try to skip stripping step, you’ll at least create deep, ugly marks on the wood surface, which very difficult to hide.