Western Hemlock
Western hemlock (Tsuga heterophylla) is the single most plentiful tree species on the coast of British Columbia. It grows along both the east and west sides of the Coast Range, from sea level to mid–elevations, as well as in the Interior wet belt west of the Rocky Mountains. On average it typically grows 30 to 50 metres tall and 1 to 1.5 metres in diameter. It seldom grows in pure stands, and is usually mixed with Douglas-fir, amablis fir, Sitka spruce, and western red cedar. Hemlock can regenerate well under a closed canopy. Hemlock makes up 17.7% of the volume of British Columbia's total growing stocks.
Common Uses
Western hemlock is commonly sold and shipped together with amabilis fir under the name Hem-Fir (also often referred to as Hem-Bal). Western hemlock is used for general construction, roof decking and plywood. It is used for laminating stock and the production of glue laminated and solid beams. Hemlock can also be used for pulp and newsprint.
Western hemlock is firmly established as an outstanding wood for mouldings and is also used for interior woodworking. Other uses include: doors, windows, interior finish, floors, suspended ceilings, ladders, and other purposes where a high-grade softwood is needed.
Western hemlock 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 | 420 |
| Air Dry | 429 |
| Specific Gravity (12% M.C.) | Standard | 0.42 |
| Hardness (N) | Side | 2740 |
| End | 4410 |
| MOE (Mpa) | Green | 10200 |
| Air Dry | 12300 |
| MOR (Mpa) | Green | 48.0 |
| Air Dry | 81.1 |
| Compression Parallel (Mpa) | Air Dry | 46.7 |
| compression Perpendicular (Mpa) | Air Dry | 4.53 |
| Shear (Mpa) | Air Dry | 6.48 |
| Cleavage (N/mm Width) | Air Dry | 37.5 |
Shrinkage
OD=oven dry
air=air dry 12% | Radial (OD) | 5.4% |
| Tangential (OD) | 8.5% |
| Volumetric (OD) | 13.0% |
| Volumetric (air) | 8.1% |
| Tang / Rad ratio | 1.6 |
Working Properties
Western hemlock has a relatively good strength-to-weight ratio and is known for its working properties. The wood requires special care when drying but yields a quality product. Western hemlock is known for its even density which provides for excellent machining properties. It turns, planes and shapes well and can be sanded to a smooth finish. The wood glues satisfactorily, has moderate nail and screw holding ability, and takes a good finish.
| Process | Performance | Comments |
|---|
| Machining |
|---|
| Planing | Fair to good results | Typical defects: Fuzzy grain, raised grain, and chip marks. |
| Turning | Good surface quality | Easy. Good results. |
| Sawing | Easy to difficult | Varies from difficult to easy. Slight to moderate blunting effect. |
| Boring | Good | Responds well to boring operations. |
| Mortising | Good | Easy. Finishes well. |
| Shaping | Moderate shaping quality | Easy, with moderate surface quality. |
| Veneering | Good | |
| Sanding | Good | Good sanding finish. |
| Fastening |
|---|
| Screwing | Moderate | Intermediate holding. Tendency to split. Good results if pre-drilled. Average screw retention: 470 lb. |
| Lateral Nail Holding | Good | Tendency to split. |
| Nail Retention | Good | |
| Gluing | Glues satisfactorily | |
| Finishing |
|---|
| Staining | Average to good | Old-growth: Smooth texture achieved. As stain gets darker, prominent wild grain is visible. A wash coat would even out the colour. Second-growth: Stainability is average for light colours, poor for dark. Best finish is with light stain or clear finish followed by nitrocellulose alkyd clear sealer and finish. |
| Painting | Average to good paint holding ability | Satisfactory paint holding ability. |
| Lacquering | Good | Old-growth: Natural finish (clear coat) looks best. Satisfactory results. Second-growth: Excellent results with clear coat. |
| Waxing | Good | Good results. Best results are obtained when using light coloured waxes (e.g. Mellow Pine). |
| Drying |
|---|
| Ease of Drying | Moderately easy to moderately difficult | There is a wide variation in the moisture content of green western hemlock. Best results are obtained when sorting by moisture content is done. Due to the high moisture content of this wood, longer kiln drying times are required. When dried at high temperatures sapwood can turn a brownish colour. |
| Durability |
|---|
| Natural Decay Resistance | Slightly durable | Not appropriate for prolonged outdoor exposure. |
| Treatability | Impermeable | Can be improved by incising. |
Commercial Availability
Hem-Fir is primarily available as structural lumber for North America, Japan and other export markets. In North America structural grades are in accordance with the National Lumber Grades Authority (NLGA) rules for dimension lumber. Select Structural, #2 and better, and stud grades are the most common grades produced for North America, with squares being the most common Japanese product. Specialty in-house grades, lamstock and export grades such as E-120 for Japan are also marketed. Western hemlock timbers are often treated for railway ties.
Appearance grades are also produced according to NLGA rules. Clears, shop lumber and moulding stock are most common, though many potential appearance grades can be produced.
Sources
BC Wood Specialties Group, www.bcwood.com
Coast Forest Products Association, www.coastforest.org