Sand blasting is where you use pressurized air to blow sand or some other appropriate abrasive particles at an object to clean it or smooth it in someway.

If you own a pressure washer you can buy a sandblasting kit to fit onto it so that you can do wet blasting.

Wet blasting differs from regular sandblasting in that you are using pressurized water instead of air to propel the sand. The main benefit wet blasting has over sandblasting is that you don't kick up a huge dust cloud when doing it.

The sand blasting kit you buy should come supplied with instructions on how to fit it. I've never used one but basically it will be a probe connected to a plastic hose that you insert into a bag of kiln-dried sand, and then you connect the other end up to your lance.

Wet blasting can be used to clean graffiti or other stubborn stains; I believe it's used for cleaning boat hulls as well. You obviously have to be careful about the surface you are cleaning when wet blasting as you don’t want to damage it.

Another good thing about wet blasting is that it decreases the need for cleaning chemicals that damage the environment.