True Quality Painters always water blasts all exterior surfaces prior to the commencement of any other work.
It’s the best way to remove the dirt and loose paint/materials.
We prefer not to use chemicals on the surfaces simply as it’s not required. Using chemicals to loosen up any moss or lichen will end up in your gardens and lawn or down storm water drains which benefits no-one. If prepared properly anyway, all moss and lichen will be removed by hand when the preparation begins.