Greg, What you say about steam being the possible cause of the extensive bubbling on top makes perfect sense; I too had wondered why the top looks so different from the bottom - although there is some slight bubbling of the underside finish underneath all the soot (see below)) and quite extensive bubbling of the paint on certain parts of the struts. Thank you for this information regarding specific temperatures related to damage; wow, those are really high temperatures! Perhaps we shouldn't in fact replace this board, but rather retain it - just sand and revarnish. One does get the impression that it must have been an event of quite short duration. I just wasn't sure what kind of damage a high but temporary might cause. Your numbers are reassuring, actually. Best regards, Allen -------------- next part -------------- A non-text attachment was scrubbed... Name: IMG_5030.JPG Type: image/jpeg Size: 2563252 bytes Desc: not available URL: <http://ptg.org/pipermail/caut.php/attachments/20100418/ed2f9e12/attachment-0002.jpeg> -------------- next part -------------- A non-text attachment was scrubbed... Name: IMG_5032.JPG Type: image/jpeg Size: 2436337 bytes Desc: not available URL: <http://ptg.org/pipermail/caut.php/attachments/20100418/ed2f9e12/attachment-0003.jpeg> -------------- next part -------------- On Apr 18, 2010, at 3:11 AM, Greg Graham wrote: > I hope you save some pieces of this soundboard and try to duplicate > the varnish bubbles in your shop. > > Laws of Physics would dictate that the top of the board could never > get hotter than the bottom when heated rapidly from below, yet the > finish on the bottom isn't bubbled. When wood is heated rapidly, > such as when burning, water is forced away from the heat. Maybe > steam caused the bubbled finish? > > Is the finish on the top different than that on the bottom? > > Regarding the possible property changes of the wood, that depends > on time and temperature. > > Commercial heat treating of softwoods is done in the 220 C range > for several hours, and results in decreased bending strength and > elasticity, but increased compression strength (think "more > brittle"). Note, though, the high temperature (220 C, not F) and > long exposure of several hours. > > The Wood Handbook says permanent changes in elasticity or strength > take months of exposure at 115 C to become significant, weeks at > 135 C, and days at 155 C. > > I would bet the temperature of your soundboard didn't get above 100 > C (converting water to steam) and only for a couple minutes. I > doubt there was any chemical or physical change to the wood. > > Greg Graham > >
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