Wood & Humidity, was Hammers

[Farrell]

Well, I don't dispute your facts. The most pertinant thing here is likely
the following:

> "End grain absorbs fastest, on the other hand and which
> abounds in actions but not so much in boards."

It's easy for me to imaging uncoated endgrain action parts absorbing
moisture much more quickly than coated soundboard cut parallel to the long
dimension.

Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com

----- Original Message -----
From: "Clark" <caccola@net1plus.com>
To: <pianotech@ptg.org>
Sent: Monday, January 01, 2001 12:33 PM
Subject: Re: Wood & Humidity, was Hammers


> Hi there, Terry,
>
> > Are we really sure that a varnish/laquer covered spruce panel
> > would absorb more moisture than an unprotected piece of
> > maple/hornbeam/walnut (or whateverelse and action is made of)?
>
> My tattered copy of the "Wood Handbook" (Department of Agriculture,
> 1955, and it came that way) gives moisture shrinkage ratios for a ton of
> stuff (more than their current pub's, maybe less than "Woods of the
> World") but not the times involved. (Do drying schedules reflect this? I
> don't have a reference as to their meanings.)
>
> Wood 20%wmc 6% 0%
> Spruce 3.8 8.0 11.5
> Maple 5 11.9 14.9
> Hornbeam 6.5 13.6 19.4
>
> (p.315-318)
>
> So far as finishes excluding moisture at 11%wmc over two weeks of nearly
> saturated conditions, the following table is given:
>
> 3 coats of Al powder in gloss oil/varnish 92%
> 3 coats Al powder in shellac 92%
> Heavy coating of paraffin 91%
> 3 coats rubbing varnish 89%
> 3 coats shellac*********************************87%
> 3 coats enamel (cellulose-lacquer vehicle) 76%
> 3 coats cellulose-lacquer 73%
> 3 coats gloss oil bronzing liquid 12%
> 3 coats furniture wax 8%
> no coats of anything 0%
>
> (p.377)
>
> Extrapolating from this in terms of volumetric expansion ratios, for an
> arbitrary 1x1x1 square at 11%wmc over an exposure period, either raising
> or lowering wmc by 2%:
>
> wood 11% +2% -2%
> Spruce 1 1.001 0.999 (shellacked)
> Spruce 1 1.008 0.992 (unshellacked)
> Maple 1 1.010 0.990
> Hornbeam 1 1.013 0.987
>
> Most probably it's not so linear or uniform, and surely these average
> values neglect differing absorption rates due grain orientation: radial
> (quarter) and tangential (flat) absorption is compared for Douglas Fir
> and SY Pine. Assuming the figures I used above are for an equal
> distribution of grain orientation, the overwhelmingly radial board
> should change dimensions more than more or less square action parts. End
> grain absorbs fastest, on the other hand and which abounds in actions
> but not so much in boards. Else that old stuff is as differr/9uas I've
> heard claimed!
>
> Does this stuff look right?
>
>
> Clark
>