[pianotech] Has anyone ever seen anything like this?

[david at piano.plus.com]

I'm pretty certain from the photos that the whiteish deposit is mildew(a
type of fungus).

http://www.fcs.uga.edu/pubs/current/C767.html

On the older uprights that abound here, you often find what one might call
"arrested mildew" on key and action.  At some point in its life the piano
has been kept in conditions where mildew has been able to thrive, and then
later the piano has changed hands and been moved to a place where the
mildew can no longer grow, but the existing powdery or whiskery residue
remains.  (The climate here is the wet of Scotland is damp, and favours
fungal growth).

To remove it, the affected parts can be wiped over with a cloth dampened
(not wet) with a proprietary mildew removing solution, or with a bleach
solution (see the website link), or in fact many household cleaning
solutions.

The crucial thing is to ensure that the ambient conditions do not continue
to favour mildew growth.  Was the piano in the photos previously kept in a
different place? If it's still in the conditions where the mildew grew,
something needs to change in order to to prevent further growth.

Options may incldue keeping the air in the room dry by the permanent use
of a small domestic dehumidifier (some models very quiet in operation, and
very effective).  Another option may be to fit a Dampp Chaser. While the
Dampp Chaser cannot remove moisture from the air in the room, by keeping
the air inside  the piano warmer than the surroundings, it prevents
moisture in the air condensing inside the piano.
Best regards,

David