The first thing that we would like to inform you about is that pressure washing is not the kind of cleaning method that usually involves the use of chemical based cleaning supplies. There is a pretty good chance that people offering pressure washing would use nothing but water since this is the long and short of what this cleaning method is supposed to incorporate. That said, if we were to take a look at power washing instead, chemical additives begin to make a whole lot more sense.
This is because of the fact that a pressure washing service that is coming to you for power washing will always try to use some chemicals so that they can make your surface squeaky clean and devoid of harmful bacteria. To answer your question, the chemical that you would need during pressure washing is largely dependent on what you are trying to do at that precise moment. The truth of the situation is that if you are cleaning a surface that does not have a porous interior structure, you should use some bleach to disinfect it.
Bleach is a popular choice when it comes to washing your home with high pressure jets or sprays of water. The fact of the matter is that it helps to remove dirt along with killing microbes that can cause all sorts of serious diseases, so you should consider using it the next time you take part in a power washing activity. This is obviously not the only chemical that you can use here, but it is certainly an option that can help you the most which is why it has gotten so immensely popular.