Swelling and shrinking of the wood
sunken joint caused by wood movement
When he release his moisture the wood will shrink, while when he absorbs water from
the air, and his moisture content is rising then he will swell. The swelling and
shrinkage of the wood can cause problems in the wood products such as: crack,
warp, uneven surfaces and other construction problems.
wood swelling and shrinking varies depend to the grain direction
The shrinkage and swelling of timber is more complicated since it varies from
one wood to another. The wood behavior, is dependent on the structure
of molecules and cells in the wood. While the cell structure depends on the
type of wood and how the wood grew. Therefore the shrinkage and the swelling is
depend on the type of wood, the origin of wood and also the grain direction. The amount of shrinkage and swelling changes with a given moisture content is
about twice as great as the flat-grain surface surface the edge grain. A wet
piece of wood will of wood shrinks more on one direction the another to distort
itself.
This different in shrinkage tendencies mean when lumber of different moisture content, species or different grain direction is glued together side by side, some pieces has risk to swell or shrink more then the other. This phenomenon is resulting on some wood construction problems such as: crack, swell, open joints, warping, defects, etc.. In the bare core for the plywood, the wood pieces with uneven volume will result on the "sunken cores" or "wash board" appearance that all the make uneven surface for the plywood veneer.
Although there may be some variation upon the origin of wood, but the shrinkage and swelling of some wood species record is already recode. The amount of volume changes will help us to understand the wood behavior and find the best way to handle it.
This different in shrinkage tendencies mean when lumber of different moisture content, species or different grain direction is glued together side by side, some pieces has risk to swell or shrink more then the other. This phenomenon is resulting on some wood construction problems such as: crack, swell, open joints, warping, defects, etc.. In the bare core for the plywood, the wood pieces with uneven volume will result on the "sunken cores" or "wash board" appearance that all the make uneven surface for the plywood veneer.
Although there may be some variation upon the origin of wood, but the shrinkage and swelling of some wood species record is already recode. The amount of volume changes will help us to understand the wood behavior and find the best way to handle it.
The amount of wood shrinkage of some species from green to dry condition ( mc 12%)
Wood species Volume Edge grain (radial) Flat grain ( tangential)
Alder, red 12,6 4,4 7,3
Ash, black 15,2 5,0 7,8
Ash, white 12,5 4,6 7,1
Ash, white, 2nd grow 14,0 5,3 8,7
Bassswood 15,8 6,6 9,3
Beech 16,2 4,8 10,6
Birch, sweet, black, cherry 15,0 6,3 7,6
Birch, yellow, gray, silver 16,8 7,4 9,0
Buckeye 12,0 3,5 7,8
Butternut 10,2 3,3 6,1
Cherry, black 11,5 3,7 7,1
Cherry, wild red 12,8 2,8 10,3
Chesnut 11,6 3,4 6,7
Cottonwood 14,1 3,9 9,2
Cucumber 13,6 5,2 8,8
Elm, rock 14,1 4,8 8,1
Elm, slippery 13,8 4,9 8,9
Elm, white or Ameican 14,4 4,2 9,5
Gum, black 13,9 4,4 7,7
Gum, blue 22,5 7,6 15,3
Gum, cotton, 12,5 4,2 7,6
Gum, red, sweet 15,0 5,2 9,9
Gum, sap (sapwood or redgum) 15,0 5,2 9,9
Hickory, shelbaark, shagbark, pignut 17,9 7,4 11,4
Hickory, pecan 13,6 4,9 8,9
Holly, American 16,2 4,5 9,5
Locust, black 9,8 4,4 6,9
Locust, honey 10,8 4,2 6,6
Maple, oregon, bigleaf,boradleaf 11,6 3,7 7,1
Maple, red, swamp, scarlet, soft 12,0 3,0 7,2
Maple, sugar rock, hard, 14,5 4,8 9,2
Mahogany, true, Central America - 3,4 4,9
Mahogany, African - 4,1 5,8
Oak, ref, yellow, Spanish,
California 14,2 4,2 8,5
Oak, white,bur, chesnut, post 15,3 5,1 9,3
Pecan 13,6 4,9 8,9
Poplar, yellow 11,4 4,1 6,9
Sassafras 10,3 4,0 6,2
Sycamore 14,2 5,1 7,6
Walnut, clack, American 11,3 5,2 7,1
Willow, black 13,8 2,6 7,8
Willow, western black 13,8 2,9 9,0
Softwood, western red 8,1 2,5 5,1
Cedar, white 7,0 2,1 4,9
Cypress, 10,7 3,8 6,0
Cypress, yellow 7,9 1,9 5,0
Fir, balsam 10,8 2,8 6,6
Fir, Douglas 11,6 4,3 7,0
Fir, white 10,2 3,4 7,0
Hemlock, eastern 10,4 3,0 6,4
Hemlock, western 11,6 4,5 7,9
Larch, western 13,2 4,2 8,1
Pine, Cubar, longleaf, western white 11,9 5,0 7,4
Pine, shortleaf 12,6 5,1 5,7
Pine, sugar 8,1 2,5 5,7
Spruce, Engelman 10,4 3,4 6,6
Spruce, red 11,8 3,8 7,8
Spruce, Sitka 11,2 4,5 7,4
Spruce, white 14,8 3,7 7,3
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