I can't recall ever seeing an outdoor sculpture get a serious cleaning. If I thought about it at all, I would have thought that rain basically does the work.
In the National Gallery of Art Sculpture Garden, there resides an almost 10 ton sculpture called Aurora, by artist Mark di Suvero. On a given day, many people stop and appreciate it for a few moments and then move on as there is a lot to see on the grounds.
But on this particular day, there was a crew with a ladder, hoses, brushes and whatnot standing on the sculpture providing a deep cleaning. I wasn't thrilled to see them standing on the actual art piece while they worked, it seemed disrespectful in a way. But I have to say, they looked almost like they were part of that sculpture! (And I guess 10 tons makes it solid for human weight of course.)
Many people stopped to watch them and then would tarry a while, commenting to each other (I suspect about the spectacle of the cleaning process). I stood at a distance and just enjoyed the novelty of this. What a special and kind of beautiful thing to witness. And truly, those workers brought the sculpture to life, albeit in a quirky way.