Chemical Damage to D-Chaser Unit

[Bill Ballard]

Dear List,

I'm swapping a Dampp-Chaser system's humidifier heater bar because 
the old one (ca. '93) rotted through. That's right, a couple of 
patches where the aluminum casing of the heater bar is simply 
missing, like lesions. Mitchell at Dampp-Chaser says the only known 
thing to do this is using non-D-C humidifier biostat. Apparently 
anything with chlorine in the tank will produce something in the 
hydrochloric acid family. (One formulation at a local hardware store 
listed ammonia chloride, as active ingredient.)

Apparently this HCl also floats upwards as a gas, rusting string. And 
there is alot of rust on the strings, tpins, and action hanger bolts 
in the top section of this Yamaha M306 Console (42", I believe). I 
immediately suspected water vapor not being properly being spread out 
by the mylar baffle tacked to the underside of the keybed. (The HM-2 
humidifier  was simply set on the piano's floor, and the narrow 
baffle was sitting  maybe 15-16" above the humidifier.) Mitchell said 
that the same caustics put on the heater bar by the wicks was also 
rising upwards from the reservoir.

The lady of the house did confirm the use of non-proprietary biostat. 
She was given an initial 8 oz. of D-C's biostat with the installation 
in '93, and when she asked that technician for a refill he told that 
any humidifier treatment off a hardware store shelf would work. 5-6 
years later, we've got rusted strings and a rotted heater bar.

The piano tuned fine: I would have been the first to complain about 
string friction. The strings do not break. The treble third of the 
action is not in the grip of corroded center pins. There is no damage 
to the wood finish, just steel parts.

The fix is simple. I already have the replacement heater bar, and I'm 
going to scrub the dust off the treble wire and the tpins. I'm 
confident of the wire (because it still tunes smoothly and doesn't 
snap), But I'd like to mic it after scrubbing it. What I do know is 
that whatever wire diameter has been lost to corrosion is not enough 
to fatally increase the wire's tension.

Has anybody run into this situation before? Is anybody familiar with 
the chemistry at work? Is my suspicion that water vapor is the agent 
here, completely baseless?

What Thinkst Thous?

Mr. Bill Ballard RPT
NH Chapter, P.T.G.

"Lady, this piano is what it is, I am what I am, and you are what you are"
     ...........From a recurring nightmare.
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