Published: 07 December, 2007
The main applications for tulipwood are furniture and interior joinery, but research into its structural potential shows it has the strength of a hardwood but the weight of a softwood. Michael Buckley of World Hardwoods reports
Tulipwood, unique as a native of North America, is a plentiful, sustainable, affordable and very flexible species. It can be stained to look like exotics, is competitive enough to compete with softwood but is harder and available in clear lengths. It can, however, be a confusing species when it comes to its name. First spotted by European settlers as tall poplar-like trees with small tulip-shaped flowers, it was named tulip poplar and later yellow poplar by which it is still known in the US. But tulipwood is Liriodendron tulipifera and quite superior to poplar and grows abundantly throughout the eastern states, concentrated in the Central and Appalachian regions.
American tulipwood is the tallest of all American hardwood trees, often growing to 100ft, although specimens have been known to reach 200ft. The diameter can vary from 2-6ft and has been measured up to 10ft, giving long, wide boards of relatively clear lumber. As a consequence of enormous seed production it is also one of the fastest naturally regenerating trees in the US and is found in pure and mixed stands.
In the UK its market history is fascinating. An early known use was at Buckingham Palace, where, in the 1930s, it was used, dark-stained, as a mahogany substitute, for fireplace surrounds and mantels. In the 1980s, in the mouldings market, it started to replace ramin, a light-coloured tropical species under threat of over-cutting in South-east Asia. Italy became a leading importer for its picture framing industry, much of which is exported to the UK and elsewhere. Tulipwood is now the number one American hardwood species in Vietnam, where it is used for furniture also destined for the UK and other European markets. Today most hardwood importers in UK have comprehensive stocks of this hardwood for a variety of uses.
The sapwood of tulipwood is creamy white and may be streaked with the heartwood varying from pale yellowish brown to olive green, sometimes with purple steaks. The green colour in the heartwood will tend to darken on exposure to light and turn brown. The wood has a medium to fine texture and is straight grained. The size of the sapwood and some physical characteristics will vary according to growing regions.
A versatile timber that is easy to machine, plane, turn, glue and bore, tulipwood dries easily, with minimal movement in performance. It has little tendency to split when nailed, and takes and holds paint, enamel and stains exceptionally well. It is a medium density wood with low bending, shock resistance, stiffness and compression values with a medium steam bending classification. It is non-resistant to decay, and has heartwood moderately resistant to preservative treatment; and the sapwood is permeable.
The vertical tulipwood curtain in the atrium of the Lex building contains core facilitiesThe main uses are furniture, interior joinery, kitchen cabinets, doors, panelling, mouldings and edge glued panels. Tulipwood turns and carves well and is suitable for spindles. In the US domestic market, tulipwood has been used as a substitute for clear softwoods in recent years. Due to its good acceptance of paint, it is widely used in picture framing, clear finished and stained or painted.
In the belief that tulipwood can be even more widely used, the American Hardwood Export Council (AHEC) recently funded a programme of structural testing of tulipwood completed at BRE. A new structural publication produced with engineers Arup, authored by Peter Ross, is now available, showing that it has the weight of many softwoods but the strength of hardwood, combined with unique aesthetics. In fact, in engineering terms, tulipwood has a density far lower than most hardwood species, however, its strength and stiffness would put it in strength category D40 (see EN 338) ranking it alongside iroko, jarrah and teak.
Considerable evidence has already been accumulated to show it can accept treatment against rot and external decay. Recent work commissioned by AHEC at BRE indicates that tulipwood has sufficient natural durability to deliver a 15-year working life for external joinery in out-of-ground contact provided a suitable surface coating was properly maintained. To satisfy a 30-year service life as, for example, laid down by the British Woodworking Federations Timber Window Accreditation Scheme, would necessitate a preservative treatment beneath a properly maintained protective finish. AHEC is now embarking on further investigations to identify a suitable commercial preservative system capable of providing this prolonged service life.
There are some interesting references for tulipwood in assessable projects. For example, tulipwood featured in St Pauls a new heart for Bow a community centre project, which was highly commended by the judges of the 2004 Wood Awards. Matthew Lloyd Architects chose it because the blondest hardwood was required. Originally the thought had been to use green oak but it was just too expensive for such a community project, and also too hard.
Tulipwood provides a stunning backdrop to the Lex officeAnother Wood Awards recognition came for a new pipe organ in St Marys Church Streatley, Berkshire, designed and built by Robin Jennings inaugurated by the Bishop of Oxford. This 11-stop organ has 16ft Bordon base pipes made of tulipwood, selected by Jennings due to its good working properties and extraordinary stability.
More recently the Lex Vehicle Leasing Headquarters in Stockport, a £5m project, required the complete refurbishment of an existing 90,000ft2 building by architects Walker and Martin. The design concept is based around creating a Social Heart, which manifests itself as a randomly shaped object and contains core facilities, and is set within an atrium-like space. Visually it appears as though a vertical tulipwood curtain has been pulled loosely around the core, so that its appearance changes as you walk around it. It provides a stunning backdrop to the office; the fluidity of the shape contrasting with the rectangular forms used elsewhere.Keywords: AHEC tulipwood species
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