1. Water and Wood

2. Water and Wood
Probably the most important but most overlooked issue facing the woodworker
Wood is Hygroscopic –The ability to absorb or desorb water
Growing trees contain a lot of water most of which is in the sap.

3. Water and Wood Two kinds of water in a growing tree:
Free water – water found in the cell cavities
Bound water – water found in the cell walls
Together they equal the Moisture Content

4. Water and Wood Calculating moisture content (MC)
WW = wet weigh DW = dry weight
WW-DW x 100 = MC DW
Red pine has 200% moisture content

5. Water and Wood
Fiber Saturation Point (FSP)- All water is removed from the cell cavities but the cell walls are still saturated.
Wood is at its weakest state at this point
It’s only when the bound water is removed that the wood begins to shrink and increase in strength.
The loss of bound water depends on Relative Humidity

6. Water and Wood 100% humidity – No bound water is lost
To remove all bound water requires an oven or vacuum at 0% humidity
In reality wood doesn’t exist in either condition
Remember – Wood is hygroscopic
As relative humidity increases the amount of bound water increases
As relative humidity decreases the amount of bound water decreases

7. Water and Wood
For a given relative humidity wood reaches an equilibrium where the amount of bound water stays constant.
This condition is called Equilibrium Moisture Content (EMC)

8. Water and Wood At 25% humidity the EMC = 5%
* EMC = 18% of relative humidity

9. Water and Wood Relative Humidity in Portland (interior)
January Relative Humidity=~ 40% EMC = ~8%
July Relative Humidity=~ 50% EMC = ~9%
Note: Any wood above fiber saturation point is considered green

10. Water and Wood Longitudinal shrinkage is negligible
Tangential shrinkage is the greatest
Radial shrinkage is lesser

11. Water and Wood

12. Water and Wood

13. Water and Wood
The difference between tangential and radial shrinkage will effect warpage.
The greater the difference the greater tendency to warp

14. Water and Wood Dim. Change from Green to Oven Dry
Stable Woods (Number represents percent of green dimension)
Tangential
Radial
Tan/Rad
Teak
4.0
2.2
1.8
Mahogany
5.1
3.7
1.4
Redwood
4.4
2.6
1.7
Potentially Troublesome
Beech
11.9
5.5
S. Red Oak
11.3
4.7
2.4
E. Pine
6.1
2.1
2.9

15. Water and Wood Methods for getting Moisture Content below FSP
FSP (average) 28%
Air Dry 14%
Kiln Dry %
Oven Dry %

16. Water and Wood
To the cabinetmaker Kiln Dried suggests moisture content below 10%
Kiln drying is needed in most locals to achieve levels appropriate for interior use
Exterior grade materials may be kiln dried to only 19% or less
Reduce weight for shipping
Kill fungus
Speed up drying process