We have a cleaning problem at the Parthenon:  some kind of calcium
deposits have formed crusts on the statuary in the east and west
pediments.  The material came from the leaking roof overhangs, dripping
through the concrete at hairline cracks.  There are no joints in the
overhangs, but water always finds a way through.  No cleaning chemicals
work, but our preference would be to soften the crusts, so that we could
gently wash away them away, without damaging the concrete or dislodge
any of the aggregate.  We are still testing.  I don't know if any of the
abbrasive systems can be controlled enough to remove the crusts, but
maybe we should begin looking at these systems, too.  Work will begin
this spring, so we need to decide...  By the way, the roof has been
replaced, including all new cast concrete tiles and metal flashing.  It
looks nice, I think, but scaffolding still surrounds the building.

Ilene