<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>Re: Plywood shrinkage??? Laminated = soundboards???</TITLE> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <STYLE type=text/css>BLOCKQUOTE { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } DL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } UL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } OL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } LI { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } </STYLE> <META content="MSHTML 6.00.2800.1276" name=GENERATOR></HEAD> <BODY bgColor=#ffffff> <DIV><FONT face=Arial size=2>Hi Ron, Del,</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial color=#000000 size=2>You're correct that the = drawer bottom panels were not coated in any way, and I suspect the original quality of = the plywood was not as good as what one has available today.  (It's a = bit hard to tell, considering the age and deterioration of the plywood.)  = I'd say that the grain orientation, at least on the outer laminates, is about = the equivalent of cheap hardware store variety material, on = average.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>I'm just curious about the moisture = blocking properties of the SB finish:  How much does the finish alter the = rate of MC change in a SB?  I presume it depends on the type and thickness of = finish used.  Has anyone done any side-by-side measurements?</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV> <DIV><FONT face=Arial size=2>Back to the plywood...</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>Regarding quality:  Although the = drawer bottoms may  be constructed of relatively poor quality material, I = would strongly suspect only the best materials are used in boat = construction.  In fact knowing some boating enthusiasts, who pour unbelievable amounts of = money into their surrogate babies, I'd suspect the quality of these materials = would rival what you builders/rebuilders use!  Furthermore, the reference = to boat deck plywood shrinkage is most likely with regard to modern-day materials.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV></DIV> <DIV><FONT face=Arial size=2>I suspect shrinkage may be the fate = under extreme conditions.  The boat deck plywood obviously gets baked in the sun, = doused with water, and so forth.  Drawer bottoms can frequently be wiped = out with wet rags -- which while not as extreme, still creates a rapid and = drastic changes in MC.  Perhaps more importantly, another dynamic is going = on in both these cases.  Deposition of water is never uniform, whether = through leakage past finish defects (boat) or through differential deposition of = water with a wet rag.  This can cause a lot of internal stress and = strain in the panel.  For instance, if a small spot in the center of a panel = is soaked with water,and the surrounding board remains dry, the swollen = center spot will be compressed within the "frame" of the surrounding wood.  = This is actually how modern "door ding" removal is done in cars, except with = heat expansion, not moisture expansion.  In the case of metal door = panels, it is a way to shrink the previously expanded metal back to its original = size.  In the case of the plywood, the compressed spot would dry out under = tension, and when other parts of the panel would later expend, the spot would gladly receed.  I suspect this may be the dynamic that results in the = progressive shrinkage of these panels.  The difference may not be quality of = plywood, so much as evenness of moisture distribution.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>It would be very interesting to model = this phenomenon with sheet metal and a blow torch, producing overall = shrinkage in the metal panel with repeated application of heat in isolated spots = throughout the panel.  Theoretically, would the panel eventually (after bizillions = of years of this sort of treatment) end up in a sphere?</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>This is a very interesting phenomenon, = to say the least!</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>Peace,</FONT></DIV> <DIV><FONT face=Arial size=2>Sarah</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV></BODY></HTML>