5 November 2013 at 11:20 pm #20920jgust747Participant
Some interesting information.
Wood shrinks most in the direction of the annual growth rings (tangentially), about one-half as much as across the rings (radially), and only slightly along the grain (longitudinally). The combined effects of radial and tangential shrinkage can distort the shape of wood pieces because of the difference in shrinkage and the curvature of the growth rings. Weight, shrinkage, strength and other properties depend on the moisture content of wood. In trees, moisture content may be as much as 200 percent of the weight of wood substance. After harvesting and milling, the wood will be dried to the proper moisture content for its end use. Wood is dimensionally stable when the moisture content is above the fiber saturation point (usually about 30 percent moisture content). Below that, wood changes dimension when it gains or loses moisture.
Different woods exhibit different moisture stability factors, but they generally shrink and swell the most in the direction of the annual growth rings (tangentially), about half as much across the rings (radially) and only slightly along the grain (longitudinally). This means that plainsawn flooring will tend to shrink and swell more in width than quartersawn flooring, and that most flooring will not shrink or swell much in length.
The numbers below reflect the dimensional change coefficient for the various species, measured as tangential shrinkage or swelling within normal moisture content limits of 6-14 percent. Tangential change values will normally reflect changes in plainsawn wood. Quartersawn wood will usually be more dimensionally stable than plainsawn.
The dimensional change coefficient can be used to calculate expected shrinkage or swelling. Simply multiply the change in moisture content by the change coefficient, then multiply by the width of the board. Example: A mesquite board (change coefficient = .00129) 5 inches wide experiences a moisture content change from 6 to 9 percent a change of 3 percentage points. In actual practice, however, change may be diminished as the boards proximity to each other tends to restrain movement.
Calculation: 3 x .00129 = .00387 x 5 = .019 inches.
.00369 Red Oak
.00365 White Oak
.00338 Yellow Birch
.00267 Douglas Fir
.00238 Santos mahogany
Found it interesting that oak and maple has more movement than pine and fir.
Dallas, Texas5 November 2013 at 11:24 pm #20921KenParticipant
interesting information Johan, thanks for posting23 December 2020 at 3:26 am #691372Jan KhmelnytskyParticipant
This is very useful information. Does anyone have ideas on how Paul’s standard shellac and wax finish might impact these coefficients. For example, could they by cut in half?23 December 2020 at 1:41 pm #691420CunhaParticipant
This is very useful information. Does anyone have ideas on how Paul’s standard shellac and wax finish might impact these coefficients. For example, could they by cut in half?
The coefficients would stay the same but the rate of change would differ. I have doors with layers of oil paint and they still move seasonally.
Different finishes have different permeability but almost all will pass water vapor. I say almost because epoxy and super thick finishes may actually block vapor transmission.
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