house stucco: What are these dark grey splotches?

I was told a pressure washer was the best way to remove these big spots...?
http://imgur.com/mMixOmP
http://i.imgur.com/mMixOmP.jpg
http://imgur.com/MZKEpo4
http://i.imgur.com/MZKEpo4.jpg
however, I was able to remove most of the spot with a large brush. Reaching the higher spots may be hard with a broom/brush.
marc
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.