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Subject: Warped wood

Warped wood

From: John Kjelland <woodobj>
Date: Sunday, July 18, 1999
On behalf of Rogier Smelt, Marie-Odile Robbins
<westdean [at] pavilion__co__uk> writes

>    I have recently been investigating methods of straightening
>    warped timbers

The correcting of aged cupped wood is really an art and can be
unpredictable. The following may give you some help. This suggestion
will most likely delaminate the veneer and is aggressive but offers
a high degree of success at flattening the oak timber. Less
aggressive procedures may be developed using these suggestions
although the outlook for success also diminishes and treatment time

Step 1 wood bending

The introduction of water to the oak needs to reach 25% (of fiber
saturation) moisture content (MC). Then steam needs to thoroughly
penetrate the timber reaching 212 degrees F (100 degrees C). This
Temperature and MC needs to remain constant for 3/4 of an hour per 1
inch if thickness. The use of a steam chamber can be used--remember
that iron (Fe) can stain the oak when wet, I use plastic pipe.
During the steaming process the timber can be pressed somewhat
beyond a flat plane into the opposite direction of the original cup,
if need be. This then should be changed to a flat plane before the
"setting process. The press needs to incorporate some stickers on
both sides of the subject timber to promote air circulation and

Step 2 The "setting" and drying

"Setting" can be accomplished in a chamber without the timber
returning to a normal MC. Humidity is not controlled although it can
be for added safety. The air temperature can be as high as 150
degrees F without sustaining any damage--though caution is advised.
To determine the length of "setting" time is hard to say. In your
case I would consider monitoring the length of time it takes for the
press to loosen from the shrinking oak and then multiply that time
by a factor of 2. Remembering to retighten the press. After
"setting" the pressed timber is placed in conditioning chamber where
the temperature is held constant at 70 to 75 degrees F. Here the
timber will dry out gently in some 2 to 3 weeks.

Then remove the press and wait a few days to see if the timber
remains flat, then reassemble the case.

The original maker of the case perhaps should have also veneered the
inside of the case as is often done to prevent this type of
distortion. There are many ethical and perhaps aesthetic reasons for
you not to add veneer to the inside, but one reason for you to do
so. If you do not add veneer the addition a sealer coat will help
slow any future cupping. I hope this is helpful. The cupping problem
can be difficult to correct. Also see Conservation DistList
Instance: 12:26, Tuesday, September 15, 1998: Water damage to wood

John Kjelland
Missoula, MT

                  Conservation DistList Instance 13:9
                  Distributed: Thursday, July 22, 1999
                        Message Id: cdl-13-9-005
Received on Sunday, 18 July, 1999

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