Vacuum Drying

[Frank Weston]

List,

As many of you know, this East Coast winter has been warm and wet, with
very high relative humidity.  After a frustrating few weeks trying to dry
an old piano with three Damp Chaser rods in an enclosure, and still reading
a RH of over 40% at the soundboard I decided to try a different approach -
vacuum bagging.

Vacuum bagging is not a new idea for assembly and laminating, but this is
the first time I have ever considered it for drying.   Essentially, my idea
was to put the piano into a baggie, and suck all the air out along with the
moisture.  I used clear 3 mil polyvinyl sheet from the hardware store and
window caulk to make the bag.  One sheet of polyvinyl over the piano was
joined by a caulk bead with one sheet of polyvinyl under.  I put some old
felt down on the soundboard so that vacuum would be relatively uniform (an
old trick from construction, otherwise the polyvinyl will form pockets). 
The vacuum pump is one I use for other manufacturing processes, but an old
refrigerator compressor would work as well.  The whole rig was connected up
with vinyl tubing and aquarium supply fittings, with an old vacuum gage
from Sears Auto thrown in to keep track of leaks and pressure (or lack
thereof).  I ran the vacuum pump continuously for a week, although after a
vacuum was drawn, RH in the bag was essentially zero.

My questions for you:

Has anyone ever done this before, and did it work?

Is there any way short of investing $175 in a wood moisture meter to
determine if the wood is, in fact, dry enough to continue with work?  One
problem with vacuum bagging is that it does not encourage cracks to open.

Frank Weston