FIBER SATURATION POINT

Also has a great flash showing the moisture uptake by wood cellulose

Moisture in wood exists in two forms: 1. Free water, liquid filling the wood cell cavities; 2. Bound water, liquid or vapor chemically bound by hydrogen bonding to the cellulose of the wood cell walls

As wood dries, the free water in the cell cavities is drawn away first. Once the free water is removed, the bound water is gradually released from the cell walls.

FIBER SATURATION POINT

Fiber saturation point (FSP): The moisture content at which all of the free water is removed - the cell cavities are empty - but the cell walls are still completely saturated.

This is a key concept in wood design since moisture affects the physical and mechanical properties of wood differently depending on whether the MC% is above or below the FSP.

* MC% above FSP: physical and mechanical properties of wood remain constant as MC% changes

* MC% below FSP: physical and mechanical properties of wood change as MC% changes

The FSP varies for different species of wood, but is typically around 30%. Table M-1 lists FSP values for various wood species. The rate of change of physical properties is also dependent on wood species.

Table M-1: Fiber Saturation Point At Room Temperature

Ash, white 24.0

Birch, yellow 27.0

Douglas fir 26.0

Hemlock, western 28.0

Larch, western 28.0

Pine, loblolly 21.0

Pine, longleaf 25.5

Pine, red 24.0

Spruce, red 27.0

Spruce, Sitka 28.5

The following demonstration is based on the properties of Douglas fir.

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