Woods to Know: Iroko | Canadian Woodworking & Home Improvement

Woods to Know: Iroko

Iroko (Milicia sp)

by Peter MacSween

Iroko is a magnificent tree found growing in tropical Africa.  Many woodworkers are familiar with it as a substitute for genuine Teak (Tectona grandis).  While it does share some visual and structural characteristics with Teak, it should also be appreciated for its own merits.
 
Typically, two species are commercially harvested as Iroko (Milicia excelsa and Milicia regia).  They typically grow to heights of 130 feet with diameters of 3 to 5 feet.  Exceptional individual trees can be 160 feet tall with 8-foot diameters.  The trunk of the tree is often clear of branches for the first 70 feet of growth.  Iroko trees will produce large amounts of lumber in excellent lengths and widths.  It also dries well with little degrade.
 
It is a diffuse pored hardwood with large pores scattered throughout the annual growth rings. This gives the wood a medium to coarse texture.  The often interlocked grain can pose problems when it is worked.  Different figure types such as ribbon stripe and curl are often found in the lumber giving Iroko lots of visual impact. 

 
The heartwood of Iroko begins as a yellow/golden colour which matures to a copper brown appearance.  The sapwood is a pale yellow and is sharply demarcated from the darker heartwood.  This colouration is similar to genuine Teak, although it lacks Teak’s dark veins and greasy feel.  Like Teak, it is a hard, durable wood that is stable once dry.
 
Working with Iroko can be easy if you learn how to deal with the interlocked grain.  Lowering cutting angles and feed rates can help reduce tear out on recalcitrant grain.  Nail and screws must be predrilled.  Given its hardness and density, care must be taken during glue ups.  Too much clamp pressure can cause starved glue joints.
 
Iroko often contains deposits of calcium carbonate.  The deposits range in size from small inclusions to large pebbles.  Obviously, care must be taken when cutting or milling Iroko as these deposits will dull tooling.  Carbide blades and cutters are a must!  Some authors claim that Iroko can sequester excess carbon dioxide in these deposits making the choice to use Iroko a way to contribute to fighting climate change. 
 
Iroko can accept most finishes.  The large pores make it a candidate for staining.  The pores will also have to be filled if you want that glass smooth finish.  For exterior projects and boats, a good quality marine spar varnish with UV inhibitors would be a good choice.  Like Teak, you can also leave exterior projects unfinished where they will age to light grey colour. 

Iroko end-grain
 
A small number of woodworkers have reported dermatitis when working with Iroko especially when it is wet.  Take precautions when working with this wood until you can determine your own reaction to it.  Use gloves for handling rough lumber and wear a dust mask when machining Iroko. 
 
Iroko is commonly used in boatbuilding, flooring, interior and exterior furniture, bench tops and any purpose where a tough wood is desired.  It is also sliced into decorative veneer.  It’s up to the individual woodworker if you want to use it as a Teak substitute.  There are issues with genuine Teak, such as price, sustainability and human rights issues.  Iroko can be a lower cost and a more responsible substitute. 
 
Iroko is not on the CITES list, but it is on the IUCN Red list.  This is due to over exploitation.  I would deal with a reputable importer that brings in wood that is sustainably harvested.  Reports imply that it is only Milicia excelsa that is threatened.  If you can find Milicia regia you can purchase it with good conscience.  Summer is almost here and Iroko would be an excellent choice for any outdoor project. 
 
 

Average Dried Weight41 lbs/ft³A measure of its weight at 12% moisture and an ambient temperature of 70°F.
Specific Gravity.66A measure of the ratio of its density compared to water (at 12% MC)
ShrinkageRadial: 2.8
Tangential: 3.8
Volumetric: 8.8
Radial (the amount of crosswise shrinkage);
Tangential (the amount of lengthwise shrinkage);
Volumetric (the total amount of shrinkage.)
T/R Ratio1.4A measure of the uniformity of tangential to radial shrinkage.
Janka Hardness1,260 lbs.A measure of resistance to denting and abrasion.
Crushing Strength7,840 lbf/in2A measure of compression strength parallel to the grain.
Colour
Heartwood is usually a yellow to golden or medium brown, with color tending to darken over time. Pale yellow sapwood is clearly demarcated from the heartwood.
GrainOpen pores with interlocked grain.
TextureMedium to coarse.
Workability
Generally easy to work, with the exception of its interlocked grain, which may cause some tearout during surfacing operations. Also, deposits of calcium carbonate are sometimes present, which can have a significant dulling effect on cutters. Iroko glues and finishes well.
Uses
Veneer, flooring, furniture, cabinetry, boatbuilding, turned items, and other small specialty wood items.
PriceContact your local dealer
For a list of Canadian retailers click here
   
Photos and Specifications Courtesy of: The Wood Database