Silica Gel Packs

[Greg Graham]

There is some good stuff in the archives about this
topic (especially Ron Nossaman's comments from Sep 6,
1998), but there is a great scientific paper available
that says it all.

Everything you ever wanted to know about Silica Gel:

http://www.apsnyc.com/pdf/silica_gel_SW_2003.pdf

What I learned from this paper:

1.  Silica Gel can be used to protect against incoming
moisture temporarily, until it takes in all the
moisture it can handle.  (This will keep your piano
strings from getting rusty in the steamship container,
if the piano is sealed in a relatively air tight
plastic bag.)  For this use, the gel is usually dried
in an oven at 100 degrees C, so it essentially starts
from "zero" moisture content.  Once it is full of
moisture, it needs to be baked to restore the
desiccant properties.  (Don't do it in your kitchen
oven!).  

2.  Silica Gel can also be used as a long-term RH
buffer, such as in museum display cases.  It will
adsorb or desorb moisture as the air from outside
leaks into the case, keeping the RH relatively
constant.  To work, the gel needs to be spread 1/4
inch or less deep on a tray for maximum air contact,
and there needs to be about 1/2 pound per cubic foot
in a tightly sealed case, allowing for about one air
exchange per day.  (In a piano, we would need to seal
all the air leaks, use some sort of impermeable finish
on the case and soundboard, and use between 6 and 10
pounds, spread thin on trays to have any significant
effect.)  

>From other 'net surfing on Silica Gel: It is not
bio-degradable.  It is not particularly hazardous,
unless you turn it to dust, which is an iritant. 
Certain brands add other chemicals to increase
effectiveness or provide a color indicator of moisture
content, which tend to be more hazardous than the
plain-jane stuff.  Don't be afraid of it, but don't
eat it either. 

So no, it doesn't have any long term effect on the
piano, good or bad.  It certainly doesn't respond fast
enough or in great enough quantity to do what a
Dampp-Chaser does for a piano.  

...Unless you can spread 10 pounds of it 1/4 thick on
trays in a tightly sealed piano. ;)

Greg Graham, RPT
in the (currently) damp and chilly Pocono Mountains