Wood of the Month:
Majestic Iroko Shares Many Uses with Teak

By Jo-Ann Kaiser


FAMILY NAME
Chlorophora excelsa and Chlorophora regia of the Family Moraceae

COMMON NAMES
Iroko, kambala, mvule, mvulu, odum, tule, intule, moreira, ireme, framere, band, semli, mandji, abang, rokko, oroko

HEIGHT/WEIGHT
Trees can grow to 160 feet with diameters of 8 to 9 feet and boles clear and cylindrical to 70 feet. Weight is 40 pounds per cubic pound with a specific gravity of 0.64.

PROPERTIES
Dries rapidly and well. Experts recommend a kiln schedule of T6-D2 for 4/4 stock and T3-D1 for 8/4 stock. Wood works easily with most machine or hand tools. Presence of calcium carbonate "stones" will add wear to cutting surfaces. Some tearing may occur with interlocked grain; experts recommend a reduced cutting angle. Wood has no odor but wet wood and wet sawdust sometimes causes dermatitis to woodworkers. Heartwood is very durable. Wood has a moderate bending rating and is not recommended for bent work.

Two species known by the commercial name iroko grow in East and West Africa. Chlorophora excelsa is found almost everywhere across the width of tropical Africa, while Chlorophora regia, shorter in height and less hardy in prolonged dry conditions, is found in West Africa, from Gambia to Ghana.

Iroko has many of the same uses of teak and is sometimes used as a teak substitute. While the tree is not related to the "true" teak, Tectona grandis, it has sometimes been called African teak or Nigerian teak.

The authors of the book The Illustrated Encyclopedia of Trees discuss iroko as a teak substitute. "The high price of teak with no likely prospect of substantial increase in volume of wood on the international market has, over the years, led to a degree of substitution by other timbers with more or less similar properties. For a long time, importers have tended to consider a 'new' timber in terms of a potential substitute for one already established. But increasing demand for wood and the availability of data from comprehensive trials by experienced timber-testing laboratories have helped to make more tropical timbers saleable under their own names." They add that for many years iroko was sold in the international market as West African teak but has now become recognized for its own properties.

A King Among Trees
"Iroko is a tree of the moist semi-deciduous forests of West Africa, and is there associated with royalty - a 'king' tree - and so generally not felled by native farmers when they are clearing forests for village agriculture," according to the Encyclopedia's editors. The tall trees are said to be majestic and the botanical name Chlorophora regia roughly translates to "royal in appearance," while excelsa means tall or high.

Uses for the wood include ship and boat building, interior and exterior joinery, furniture making, cabinetry and carving. It is used to make decorative veneers and for making plywood. It is also used as a structural timber and its properties make it popular for use as railroad ties, piling and other marine work. Iroko is also used as domestic and parquet flooring.

The color of the wood from the tree varies from golden orange to light brown, to a rich golden brown. The tree has a pale yellow sapwood and a darker heartwood that, like teak, darkens with age in shady conditions but bleaches in the sun. Experts say that the fact that iroko bleaches in the open air and sun makes it a good substitute for teak in uses like boatbuilding and outdoor furniture. The wood's grain is usually interlocked and sometimes irregular with a coarse texture. The wood can contain hard deposits of calcium carbonate, sometimes called stone. If the calcium carbonate deposits are present, they are usually detectable because they are surrounded by darker material. The stones are sometimes large and hard and will damage saws and other cutting tools. Experts recommend the use of tipped or hardened saw teeth when cutting iroko.

A Good Teak Substitute
Iroko, according to The Encyclopedia of Wood, "lacks the greasy feel of teak" yet it has enough similarities to make a good substitute. Iroko is harder but slightly weaker than teak. Among the uses they share are garden and park bench seats. It is also used for counters and laboratory bench tops and draining boards, because of its durability in wet conditions. Albert Constantine, Jr., in the book Know Your Woods, writes that quartered iroko is used for furniture and architectural panels.

Other teak substitutes include cordia (Cordia alliodora) and afrormosia (Pericopsis elata). While teak grows well on plantations, iroko has not had that success, according to the authors of The Illustrated Encyclopedia of Trees.

Working Challenges
Iroko poses some health problems to workers. Exposure to wet wood and sawdust can cause dermatitis and fine machining dust can irritate skin and nasal passages, and is especially dangerous to workers with asthma.

The sapwood is vulnerable to attack by insects, especially the powder post beetle, but the heartwood is very durable. The heartwood resists preservatives; its sapwood can be treated. Outside of the problems associated when "stones" are present, the wood works well with most tools. The interlocked grain can pose problems in cutting and a reduced angle of 15 degrees is suggested. The wood nails and screws well. It will finish well, but experts recommend filling for the best results. The wood dries fairly quickly and well with few problems, but stick marks sometimes result. The wood has small movement in service.

One quirky thing about the tree is what happens after cutting. When freshly cut, the stump oozes a clear resin that covers the cut area and hardens, forming a glass-like surface that retards decay.

                                                                                                                                                                                           

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