Relative Stability in Wood Species and Grain
When restoring old solid planking, deck houses, or any application using large crossgrain expanses or wood, for a number of reasons it's often difficult to match the species or grain of wood used in replacement planks. Why this is important are the potentially dramatic differences is seasonal expansion and contraction rates between species and between flatsawn, quartersawn or riftsawn wood. Get it wrong and you can create leaks, strain or break fasteners, or even buckle a plank.
As a forest biologist I'm much better trained in growing trees than in engineering, but I'm also a third-generation boatbuilder who ends up doing wood technology consulting by default. ;) I devised the table below for a boatyard often called on to mix and match wood species and grain. It uses USDA green to oven-dry shrinkage data as indicators of relative stability between species. The data is listed by the radial shrinkage qsawn lumber exhibits, the tangential shrinkage flatsawn lumber exhibits, and an average of radial and tangential shrinkage that riftsawn lumber having growth rings at 45 degrees exhibits.
http://pic20.picturetrail.com/VOL12/.../364231046.jpg
Again, these are relative figures that have been shown to correlate to normal seasonal movement, and are based on averages of hundreds of samples tested by the Forest Products Lab since the beginning of the last century. Keep in mind however, that there are few absolutes in nature, and any individual tree or stick of wood can vary with these figures by as much as a third.
As a practical example, consider an old boat planked in flatsawn Northern White Cedar, a relatively small tree of limited range that's often difficult to find in the cuts and widths required. It's green to oven-dry shrinkage is 4.9% in flatsawn, so potential matches include flatsawn Khaya at 4.5%, flatsawn redwood at 4.9%, flatsawn WRC at 5 %, flatsawn ERC at 4.7%, qsawn Spanish Cedar at 4.1%, etc. Among potential matches sort for hardness, weight and availability, and flatsawn WRC is the best choice.
Quote:
Order of Stability in Wood Species
Percent Shrinkage Green to Oven Dry as an Indicator of Relative Stability
Radial
Tangential
(R+T)/2
Northern White Cedar 2.2
4.9
3.5
Honduras Mahogany 3.0
4.1
3.5
Khaya 2.5
4.5
3.5
Redwood, 2d Growth 2.2
4.9
3.5
Western Red Cedar 2.4
5.0
3.7
Eastern Red Cedar 3.1
4.7
3.9
Atlantic White Cedar 2.9
5.4
4.1
Eastern White Pine 2.1
6.1
4.1
Teak 2.5
5.8
4.15
Incense Cedar 3.3
5.2
4.25
Alaska Yellow Cedar 2.8
6.0
4.4
Purpleheart 3.2
6.1
4.65
South American Cedar 4.0
6.0
5.0
Iroko 4.0
6.0
5.0
Sassafras 4.0
6.2
5.1
Okoume 4.1
6.1
5.1
Spanish Cedar 4.2
6.3
5.25
Black Cherry 3.7
7.1
5.4
Black Spruce 4.1
6.8
5.45
Tamarack 3.7
7.4
5.55
Baldcypress 3.8
6.2
5.6
Port Orford Cedar 4.6
6.9
5.75
Dark Red Meranti 3.8
7.9
5.85
Black Locust 4.6
7.2
5.9
Sitka Spruce 4.3
7.5
5.9
Sapele 4.6
7.4
6.0
Douglas Fir 4.8
7.6
6.2
Longleaf Pine 5.1
7.5
6.3
White Ash 4.9
7.8
6.35
Black Ash 5.0
7.8
6.4
Yellow Poplar 4.6
8.2
6.4
Rock Elm 4.8
8.1
6.45
Slash Pine 5.4
7.6
6.5
Apitong 4.6
8.2
6.5
Light Red Meranti 4.6
8.5
6.55
Black Walnut 5.5
7.8
6.65
Tangile 4.3
9.1
6.7
Western Larch 4.5
9.1
6.8
Angelique 4.6
8.2
7.0
Ipe 6.6
8.0
7.3
White Oak 5.3
9.1
8.0
Live Oak 6.6
9.5
8.0,
Greenheart 8.8
9.6
9.2
