You are wrong again ... it is not you being derided, It is you showing
up here, making a statement that is misleading, and taking exception to
being corrected (and very nicely and politely so, if you read my first post)
What we don't particularly care for here is misleading information, so
pardon me if I don't feel sorry for your above whining as somehow being
Well, that's self-serving to the max. You might as well say that the
physicists on believe Newton's Principles; after all, it's "only" a theory.
I suggest you do read Hoadley (or any of several references from the US
Forest Products Lab, these can be downloaded at no cost); specifically
Chap 4, "Wood and Water".
The short story is---wood shrinks as it dries and it does so
non-uniformly. The tangential/radial shrinkage ratio from green to
oven-dry has been measured for some hundreds of species and averages
about 2 (roughly an average of 8%/4% T/R) but shows a significant
variation between species of from just barely above 1:1 to highs
approaching 3:1. The higher the ratio the more the particular would
will distort as it is dried as the relative shrinkage in the two
directions competes at a different rate.
The difference between tangential and radial shrinkage isn't random nor
magic; it's caused by the anatomical structure, principally the effect
of wood rays whose lengthwise axes are oriented radially outward.
Species w/ more predominant rays are more stable.
Over the range of moisture content shrinkage is roughly proportional to
moisture loss. This doesn't matter too much as raw lumber is dried; the
roughsawn stock is oversize to begin with and if dried uniformly will be
stable after it is milled given a uniform environment. This is why it
is so important to finish both sides of a furniture panel, say--if one
side is finished and the other not, differential moisture absorption is
highly likely to cause movement.
Cupping after the fact is owing to one of two causes--either the piece
wasn't at equilibrium to begin with and dried after milling with the
resultant change in dimension as determined by the species' particular
T/R ratio and the percentage change in moisture.
The second is that the piece has subsequently absorbed moisture and
therefore grown. The relative amount in the direction is also dependent
on T/R and how uniform (or un-uniform) the moisture absorption is.
Cupping in flatsawn boards results in concavity away from the pith, the
result of greater tangential than radial shrinkage. The magnitude is
greater as the location of the board from the original trunk is closer
to the pith on a surface. This face is completely radial while the
opposite is tangential in the portion across from the location of the
pith and will therefore shrink at twice the rate. Woodworkers tend to
say the "rings flatten out" which an easy way to remember the direction
the board will cup but the reason for the cup has virtually nothing to
do w/ the growth rings themselves.
Cup is reversible on swelling which is why the idea of wetting is given
as a cure. Of course, the end then has to be to get the whole board in
equilibrium again at that point which goes back to point a) above--if
the piece was milled in inequilibrium, it's an insoluble problem w/o
Very interesting and valuable information. But I'm not sure it's particularly
relavent to my situation.
If it is warped, simply putting under great pressure (I have a few thousand
pounds of red bricks at hand), it's probably not pertinent *which* way it's
Placed on small square lumber and weighted, should give some good results.
You can press it flat all you want but unless you change either the
moisture content back to equilibrium at the time it was milled and
(presumably) flat or, if as noted previously, it was milled while not in
an equilibrium moisture content where it now is it will just return to
the present shape again.
If you can restrain it sufficiently, you _may_ be able to hold it in place.
This doesn't hold water ;-) when speaking of this table top. The bottom is
not likely to be "soaked" in water but free to dry, much more so than the
top. The top is exposed to water (rain, spillage), whereas the underside has
little exposure to water except for the little that drips around the edges of
the table and which gravity will pull it off immediately.
The bottom side of the table top looks nearly pristine, whereas the top looks
like it's been through a war: the factory finish (polyurethane?) is still on
the underside of the wood but long since baked off the top (from sun
You obviously did not bother to read the very specific quote at the end
of my post that deals with "sun exposure". LOL
You're right that what you quote above does not apply to your table
...nor was it ever intended to.
What does indeed apply to your table is the description you used in your
original post ... the term "weathered".
You might want to go back and read the second "example" I used for the
effects of moisture on the dimensional stability of wood, as well as the
quote at the bottom which specifically deals with wood subjected to sun
If you did not accurately describe the condition of your table, then you
have no one to blame but yourself for misapplying the examples. :)
Just so there is no mistake how appropriate the quote was to your table
suffering "sun exposure" (sic), here it is again:
Wood warmed by the sun experiences a virtual RH far below the ambient
RH. The surface dries faster than the rest of the lumber. This is why
cupping and checking often occur on decking boards; the top surface is
much drier than the rest of the board. Shrinkage of the top surface
commensurate with this dryness causes cupping and checking parallel to
It really does help to read an _entire_ post, not just those parts you
want to take exception to. :)
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Then I tried "sticker wood" and got this and the like:
There comes a point where the flaming of "Don't you use Google?" is worth
Whatever will allow air movement and keep it basically flat (flat is
relative really - a wal-mart straight edge is "flat" - unless of course
you compare it to a $45.00 straight edge - which is more flat :) ).
Let me clarify (at the danger of possibly being accused of trying to
change tack) what I meant when you asked "concave moist side". I meant
yes - as in moist side that has dried. I did not mean simply the moist
side causes a cup - it would have been made moist while compression was
placed on it (i.e. the dry side) and then dry out (but it may also take
many many times of this before a cup is seen). Information that is only
needed if someone is interested - from books - and not even needed to be
mentioned to answer your OP - so I guess my headache was caused once
again be me :)
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