Wood & Humidity, was Hammers

[Clark]

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