An article by Peter Kaczmar, TRADA Technology, published in TRADA Timber Industry Yearbook 2000.
Current trends within the timber industry show shifts in emphasis of the timber species being marketed. Traditionally used tropical rainforest species are increasingly being replaced by alternatives from other sources for a variety of reasons. The selection of these alternatives is driven by a range of considerations such as consistency and sustainability of supply, durability, cost, machinability, weight, texture, their ability to accept wood coatings and accessibility of information relating to their properties.
Figures for tropical hardwood imports and consultations with a number of major British importers suggest that meranti, keruing and Brazilian mahogany are still the major primary species dominating the UK market. However, inclusion of species such as Brazilian cedar would reinforce the view held by many that the UK timber market is beginning to respond to factors favouring the importation of alternative species. Similar indications with temperate hardwood imports are occurring where the emergence of species such as American yellow poplar and American cherry indicate a trend towards the greater use of secondary hardwoods.
The use of terms such as “alternative”, or “secondary hardwood species” at present is relatively meaningless, as there appears to be no consensus on their definition. From a purely commercial context the term “alternative “ species seems to be anything that is not currently in popular usage. To the consumer, such terms assume a more philosophical guise conjuring up the concept of timber supply from managed sources.
The combined pressures of increasing cost, maintaining consistency of supply and to a lesser extent environmental impact have resulted in a change of emphasis with respect to the manner in which species are selected. Importers are no longer looking to find closely matching substitutes for Brazilian mahogany in terms of workability and performance in-situ, but rather a readily available substitute for meranti with price advantage and comparable colour.
Whilst considerations of natural durability still continue to be of importance in today’s economic environment, increasingly these are assuming a subsidiary nature in the selection process. This is because the availability of modern preservative pre-treatments, sophisticated finishing systems and greater consideration to aspects of functional design can, to an extent, contribute to ensuring long-term performance.
The problem with the trend towards alternative timber species is that consumers have not moderated their demands and expect new species to possess similar visual characteristics to those of currently used or more traditional timbers. In short, consumers have grown to expect Brazilian mahogany “look-alikes” for their timber doors. This is one reason why meranti has been adopted in the joinery sector as an alternative substitute. However, problems with consistency of supply and added value at source have steadily eroded the market advantage of meranti to the point where other alternatives are being sought. The problem with these alternatives is that their colour characteristics often differ substantially from the richness of colour offered by Brazilian mahogany or meranti, requiring the application of pigmented semi-translucent stain systems to produce an acceptable mahogany look-alike.
It is possible that new species alternatives will be selected as much on the basis of their ability to accept translucent stains and other coatings as on considerations of weight, cost and supply.
It is well known that each timber exerts its own specific influence on exterior coatings when exposed to long-term weathering. Effects with timbers such as teak, iroko, birch and oak may range from protracted drying, fracturing and checking of the finish to severe mould disfigurement due to the presence of sugars and organic extractives which provide a nutrient source. Where literature on coating performance is available, it is mainly confined to aspects of paintability and short-term acceptance of the coating by the timber. There is little or no information on the long-term behaviour of finishes on secondary hardwood species.
The consumer or specifier who is expected to select appropriate finishes for these new substrates is left with the task of predicting long-term performance of currently available wood coating systems on the strength of their expected performance on primary hardwood or softwood species. Without the availability of appropriate information on the performance of coatings on new hardwood species such a specification strategy is likely to have costly maintenance implications.
In order to develop appropriate long-term predictive performance information, TRADA Technology has studied the long-term performance of exterior wood finish systems on alternative hardwood species. The research was supported by the Department of the Environment, Transport and the Regions and TRADA. A range of generic wood finishes was applied to selected lesser-known hardwoods considered to have market potential as alternatives to traditionally used tropical rainforest species.
Selection of species for the trial was based on discussions with large importers, users of hardwoods and trade associations. Species considered to have the greatest commercial potential were selected using factors such as texture, machining qualities, straightness of grain, liability to distortion, weight and paintability (and/or the ability to accept stains where such information existed). Wherever possible selections were made using environmental criteria, although in the absence of reliable information these were often speculative.
Whilst it was not the intention of the programme to consider specific end-use requirements, many, though not all, selections were made on the basis of potential suitability within the UK joinery sector. This was done on the grounds of the relative importance of joinery within the timber industry and the fact that it requires a relatively high proportion of durable timbers so as to maintain compliance with the requirements of BS EN 350 Durability of wood and wood-based products. Examples of timbers likely to be used in heavy constructional end-uses were also included.
Seventeen species were selected for their commercial potential for use as joinery and constructional timbers. They were tested with nine different coating formulations differing fundamentally in chemical constitution and physical properties and compared with three reference timbers (European redwood/Scots pine, iroko and sapele) with a known track record with regard to their reaction to coatings and which, together, served as a performance datum.
Selection of timber species
Idigbo Terminalia ivorensis A.Chev.
Tatajuba Bagassa guianensis Aubl.
Kamarare Eucalyptus deglupta
Afzelia Afzelia africana Smith
Durian Coelostegia griffithi
Andiroba Carapa guianensis Aubl.
Agba Gossweiledendron balsamiferum Harms.
Brazilian Cedar Cedrela odorata
Tauari Courataria oblongifolia
Dahoma Piptadeniastrum africanum (Hook f.) Brenan.
Purpleheart Peltogyne porphyrocardia Griseb.
Tornillo Cedrelinga cataeniformis Ducke
Curupixia (“Corubixia”) Micropholis gardnerianum
Quarubarana Erisma lanceolatum Stafl.
Yellow Hardwood Neonauclea spp.
American Red Oak Quercus rubra Du Roi
Tulipwood Liriodendron tulipifera L.
The results of this work, published in the TRADA Wood Information Sheet Exterior coatings on alternative hardwoods enable designers and specifiers to make a more informed choice when assessing the options for alternative timbers.
