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Subject: Warped wood

Warped wood

From: Terry Conners <conners>
Date: Tuesday, June 22, 1999
Regarding Rogier Smelt's warped wood problem, the problem is not
that the core wood is faced with cross-banded veneers, the problem
is that there has been a moisture imbalance that caused the wood to
bow due to differential moisture adsorption or desorption. The
application of water or water vapor/steam to the concave surface
will plasticize and swell the wood, and if it is allowed to re-dry
under a load (sufficient to straighten out the board if possible)
then it should remain in the dried shape barring future moisture
problems --perhaps the loading step was left out in previous
straightening attempts? BTW, both moisture and heat act as
plasticizing agents by themselves, but heat and moisture together
act as the best plasticizing agent. For example, steaming is how ash
ribs are shaped for canoes (and they are allowed to dry/cool on a

Additionally note that if the case was originally assembled with
veneers and substrate at very different moisture contents then the
moisture imbalance originated with the maker and the warping would
have arisen soon afterwards--perhaps the core board by itself had a
moisture imbalance. Adding either heat or moisture to the
(protein-based?) adhesive used to hold the veneer to the substrate
may cause the adhesive to fail--be cautious or be prepared to
attempt further repairs.

Terry Conners
Associate Professor
Forest Products Laboratory
Box 9820
Mississippi State University
Mississippi State, MS 39762 USA

                  Conservation DistList Instance 13:3
                  Distributed: Thursday, June 24, 1999
                        Message Id: cdl-13-3-005
Received on Tuesday, 22 June, 1999

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