A timber of two halves
Published: 10 December, 2006
American ash is the ideal hardwood for anything from construction through to joinery and furniture. Michael Buckley of World Hardwoods explains
Ash, like oak, is one of the great temperate hardwoods However, if ash has any edge over oak, it is the colour, grain and extrovert character that it offers to designers.
American ash is mainly white ash, Fraxinus americana, but includes black or brown ash, Fraxinus nigra. This is sometimes the root of confusion, for the heartwood of white ash is also frequently referred to as brown ash. The percentage of brown heartwood in americana depends very much on growing location. For example, in the faster-grown southern ash there is a smaller proportion of heartwood than the slower grown, colder climate northern ash and the density varies too.
White ash is often sold as northern or southern. Its provenance extends from New England to Florida in the east and as far west as Minnesota and eastern Texas. So the old adage, when specifying American hardwoods, is know your source. Most European hardwood importers and distributors are well versed in their different characteristics.
Ash represents about 10% of the American hardwood sawn timber imported into the UK, making it the second most popular after white oak, and in the first six months of 2006 UK imports were valued at US$4.7m. This compares with 6% for Europe as a whole, where ash is number four or five.
One of the earliest uses of American ash was as a snake repellant, with hunters putting leaves boots and pockets. Since then the timber has become best known for its use in baseball bats, tool handles and anything where wood needs to be bent or absorb shock. The tree grows to 70 or 80ft, rather larger than its European cousin, and produces long, wide boards, relatively defect -free. Ash may represent only 4.5% of the total standing hardwood resource (Source: USDA/FAS, 1992) but that nevertheless amounts to 373 million m3. Ash has been harvested continuously since settlers first arrived and yet it increases its growing volume by sound management and natural regeneration a true measure of sustainability.
The Sage Gateshead is lined with solid woodIn his book World Woods in Colour, WA Lincoln (ISBN 0 85442 028 2) describes American ash as weighing around 660kg/m3 with very good bending properties, good strength, elasticity, toughness, stiffness, and hardness qualities allied to its relatively light weight
and excellent shock resistance. This was enough to encourage the American Hardwood Export Council in Europe to select ash, along with red and white oak and tulipwood, for structural testing by BRE several years ago. The results are published in Structural Design in American Hardwoods, which provides architects and engineers with structural data under Eurocodes not previously available.
American ash is classified as non-durable, although the sapwood is permeable and easily treated with preservative, whereas the heartwood is moderately easy to treat. This fact also enables American ash to be more easily treated with fire retardant chemicals than some other hardwoods. For example, using the heartwood treatability designations given in EN 350-2, TRADA lists American ash as being Class 1, easy to treat, while European ash is listed as Class 2, moderately easy to treat. This better permeability of American ash leads to a greater uptake and retention of chemicals necessary to achieve the Class 0 fire rating demanded by Building Regulations for internal linings used in escape routes and circulation areas in public buildings.
Other properties lead to the harder wood needing pre-boring for nails, but it machines well and also glues, stains and polishes well to a fine finish. The decorative properties of ash are derived from its strong grain patterns and generally warm colour, which varies from pale to yellow.
Ireland's Office of Public Works used ash in the Marine Institute in GalwayThere are many references for the use of American ash. Joan Bakewell's kitchen in Fulham won a Carpenters' Award for the white ash joinery some years ago. A whole generation of young people grew up with black ash furniture, a fashion that still lingers today. Many shopfitters have used the species to good effect in high street renovations for building societies and banks; and at airport shopping facilities where natural light is minimal or non-existent. Wherever a light and airy feel is needed, designers have turned to this fresh looking wood.
In performance its hardness makes it ideal for flooring and, with its distinct grain pattern, it shows wear and tear less than some other light species such as hard maple.
Its most recent recognition was the FSC-certified white ash specified by Foster and Partners in the Sage Gateshead (Timber Building volume 1 2006. The conference and concert auditorium, seating an audience of 1,700, was completely lined in solid wood to a very complex curvature which required the assistance of TRADA for the work done by Abrahams and Carlisle in Bradford. This highly experienced joinery contractor used an MDF base to make up the profile, with ash providing the visual and acoustical surface.
The Office of Public Works in Dublin also specified ash for its highly acclaimed EU Veterinary Office and more recently in the Marine Institute in Galway (Timber Building Summer 2006).
Is timber well placed to benefit from the opportunities presented by the London 2012 Olympics?