Sitka Spruce
Sitka spruce (Pinus sitchensis) grows along the Coast in a narrow band. It is most common along the coastal fog-belt and river and stream flood plains. It attains its best development on the Queen Charlotte Islands. This tree is the largest of the spruces and grows up to 70 metres tall and 2 metres in diameter. While Sitka spruce grows in pure stands, it is also found common mixed with Douglas-fir, western red cedar and red alder.
Common Uses
Sitka spruce is used in a variety of structural products. High grades of Sitka spruce are popular for specialty marine applications such as masts, spars and deck beams, and for ladder stock and industrial equipment where a high strength-to-weight ratio is desired. During the First World War this species assumed great importance for airplane construction.
Clear grades are used in fine interior finishing such as sliding screens, mouldings, joinery and trim. It is particularly popular when an even-coloured natural wood finish is desired. The top grade clear wood is used for piano and guitar sound-boards as it has excellent resonating properties.
Sitka spruce lumber is dried according to end-use and customer specifications. Kiln drying inhibits natural staining of the wood, improves its strength and stiffness, enhances its appearance, and increases its resistance to decay and attack by insects.
| Physical Properties |
|---|
| Density (kg/m3) | Green | 347 |
| Air Dry | 387 |
| Specific Gravity (12% M.C.) | Standard | 0.35 |
| Hardness (N) | Side | 2200 |
| End | 3090 |
| MOE (Mpa) | Green | 9450 |
| Air Dry | 11200 |
| MOR (Mpa) | Green | 37.4 |
| Air Dry | 69.8 |
| Compression Parallel (Mpa) | Air Dry | 37.8 |
| compression Perpendicular (Mpa) | Air Dry | 4.10 |
| Shear (Mpa) | Air Dry | 6.78 |
| Cleavage (N/mm Width) | Air Dry | 38.0 |
Shrinkage
OD=oven dry
air=air dry 12% | Radial (OD) | 4.6% |
| Tangential (OD) | 7.8% |
| Volumetric (OD) | 11.7% |
| Volumetric (air) | 6.0% |
| Tang / Rad ratio | 1.7 |
Working Properties
Sitka spruce has a high strength-to-weight ratio and is well known for its working properties. The wood dries rapidly with small dimensional movement and little tendency to check. It is relatively easy to work, with good machining qualities. It planes and shapes well and can be sanded to a smooth finish. The wood glues easily, has moderate nail and screw holding ability, and takes a good finish.
| Process | Performance | Comments |
|---|
| Machining |
|---|
| Planing | Excellent planing quality | Recommended planer settings: 12o hook angle and20 kmpi (knife marks per inch). Takes a smooth silky finish provided sharp tools are used. |
| Turning | Medium to low surface quality | Common defects: torn out grain. |
| Sawing | Easy to work with tools | Easy to work provided cutting edges are kept sharp and the wood is free of knots. |
| Boring | Medium | Medium to good boring quality with brad point bits and lower quality with single twist bits. |
| Mortising | Good | Good mortising quality when using both chain and hollow chisel mortises. |
| Shaping | Good shaping quality | Recommend the use of a counter piece for end-grain shaping. |
| Veneering | Good | |
| Sanding | Good | Excellent sanding quality. |
| Fastening |
|---|
| Screwing | Moderate | Average screw retention: 402 lb. |
| Lateral Nail Holding | N/A | |
| Nail Retention | Good | |
| Gluing | Easy | Bonds very easily with adhesives of a wide range of properties and under a wide range of bonding conditions. |
| Finishing |
|---|
| Staining | Easy to moderate | Smooth finish achieved. Light stains work well but dark stains magnify the uneven colours produced by different textures in wood. A wash coat would even out the colour. |
| Painting | Average to good paint holding ability | |
| Lacquering | Good | |
| Waxing | Good | Best results are obtained when using light-coloured waxes (e.g. Mellow Pine). |
| Drying |
|---|
| Ease of Drying | Easy to moderately easy | Dries rapidly and quite well, but care is required to reduce warping, splitting and loosening of knots. |
| Durability |
|---|
| Natural Decay Resistance | Slightly durable | Not appropriate for prolonged outdoor exposure. |
| Treatability | Impermeable | Can be improved by incising. |
Commercial Availability
In North America structural grades are in accordance with the National Lumber Grades Authority (NLGA) rules for dimension lumber. Sitka spruce is currently marketed under the Northern Species group making its official structural design value lower than SPF, Hem-Fir, or DFir-Larch.
Sitka spruce is commonly produced in appearance grades according to NLGA rules. Clears, shop lumber and moulding stock are most common. Sitka spruce is also offered in export grades for Japan and other markets.
Sources
BC Wood Specialties Group, www.bcwood.com
Coast Forest Products Association, www.coastforest.org