03 November 2010
American hardwood lumber grading Q&A series: September & October 2010
by Bob Sabistina- Grading consultant to the American Hardwood Export Council (AHEC)
The Grading Rules for North American hardwood lumber were established over 100 years ago by the National Hardwood Lumber Association (NHLA), which is has its headquarters in Memphis, Tennessee.
I have been writing a series of articles, answering a variety of questions pertaining to the application of those grading rules. Here are some more answers to questions received from the many hardwood traders and end users I have met around the world in the past few weeks.
Question 1: I have a small cabinet shop in India and often receive offers for hardwood lumber from America. The problem I have is that I think this lumber is being imported to India in log form and milled and dried here. How can I be sure that this wood has truly been processed in America?
Answer 1: Let me start with full lifts of kiln dried lumber. American mills typically sort the wood by lengths; two lengths per pack, such as 9 and 10 feet or 11 and 12 feet. The boards are normally double-end trimmed and coated with a wax-based paint to prevent end-checking.
Most exporters have a company logo they paint on the side of each package to differentiate their stock from others when placed in a warehouse. All of these visible features, however, can be easily duplicated.
The most important issue is moisture content (MC). With a hand held moisture metre, readily available throughout the world, you can verify the MC of the wood being offered. In America, mills typically dry the lumber to a MC of between 6 and 9%. Even if the wood takes on moisture on the long journey to India, it should not pick up more than two or three percentage points. In my experience, the ideal MC range for India is around 11-12%, but I am sure you are aware of this in your cabinet shop. If the wood being offered meets all of the above criteria, then it probably doesnít really matter where it was manufactured.
Question 2: We recently purchased some 6/4 (38.1 mm) No 1 Common ash. When carrying out our receiving inspection we noticed a significant number of pieces that were less than 38mm. I asked my supplier about this and he says the NHLA grading rules allow this kiln dried wood to be thin. Please explain this to me.
Answer 2: As we all know, when going through the drying process, hardwood lumber will shrink in volume. The NHLA grading rules recognize this shrinkage both in width and thickness. The minimum widths allow for up to ľ inch (6.35mm) shrinkage, while the thickness is allowed to be 1/16 inch (1.58mm) less than the standard rough sawn thickness.
This is one of the reasons that most mills target a 1/16 inch over-thickness when converting logs to lumber. If you need a net thickness of 38mm after kiln drying, you should specify this in your purchase order.
Question 3: I have a cabinet and flooring manufacturing business in Tianjin, China. I buy a lot of Russian timber and there are times when they tell me they cannot supply me any wood. I am very interested in American hardwoods and wonder, will this also be a problem?
Answer 3: Few other countries can boast the success America has had in the sustainability of its hardwood forests. The last 80 years of improved forest management and state and federal regulations, together with greater silvicultural understanding and public desire to conserve forests, have resulted in a dramatic recovery and renewal of the American hardwood resource. The hardwood sawmilling and processing industry, which depends upon this
resource, is the largest producer of sawn hardwood in the world. In recent years, the U.S. has substantially increased exports and through careful management of its forests, the United States is growing more hardwood each year than it harvests, ensuring reliable and long term supplies.
The net volume of hardwood growing stock in the USA has increased from 184,090 million cubic feet in 1953 to just under 400,000 million cubic feet in 2007 (Resource Planning Act Assessment 2007).
In short, this means that you can be absolutely certain of the long term availability and ready supply of American hardwoods.
Question 4: I attended a grading seminar that you gave last year in Indonesia. I wonder about the number of cuttings allowed for each grade, which is shown in the grading chart at the back of the AHECís The Illustrated Guide to American Hardwood Lumber Grades. Could you explain how this works?
Answer 4: My simple answer is not to worry about them. In reality, the number of cuttings is a moot point, because on the vast majority of pieces in a lift of hardwood, there are only a finite amount of clear areas available. No matter the grade, the board will only have the amount of clear cuttings available to make the particular grade. Yes, there are a few exceptions to this rule, but in the big picture you will not need to think about how many cuttings are available, but more about how many cutting units are required to give you the percentage needed for each grade.
David Venables durante la conferenza svoltasi a Istanbul