Design Solutions - Spring 2008 - (Page 56) In the past some specifications for preservatives called for “a 3-minute dip in a 5% solution of penta-chlorophenol,” but this is no longer appropriate. Take a look at your office master and remove those references if they are still there. There are treatments available which are environmentally acceptable. Check with local manufacturers to find out what they are using. In fact the best protection for woodwork of any kind is to keep it dry and paint it well. There is no such thing as “dry rot” in woodwork. The decay of fine woodwork is almost always associated with the bacteria which thrive on moist wood fibers. L u m b e r S p e c i f i c at i o n S How to Select Solid Lumber Figure 100-06, page 26, Quality Standards Ilustrated Remember, lumber is a raw material. Lumber itself is not properly specified using the AWI Quality Standards terms Premium, Custom or Economy Grades; these grades apply only to finished work. Unlike other areas of construction, calling out architectural woodwork and millwork lumber by industry grade, such as the National Hardwood Lumber Association (NHLA) grading system, is not appropriate either. The reason for this is that the top NHLA grade FAS hardwood rules only require about 85% clear cutting in any board. Including NHLA grades in your project specifications for interior architectural woodwork could allow your contractor to deliver boards with 15% of the surface containing knots and splits. Specify your woodwork products using the AWI Grade of work appropriate for your project. The lumber grade flows directly from that selection and will be the responsibility of the woodworker, as you will learn below. Specifications should also avoid using the AWI terms for grades of lumber, shown as Roman numerals I, II, and III. Unless you need to 56 DESIGN SOLUTIONS make a change in the lumber grade, leave the selection of lumber grade to the requirements established by the Quality Standards. Lumber thickness is measured in “quarters” of an inch. Rough lumber one inch thick would be called 4-quarter; 1-1/2 inch lumber called 6-quarter, etc. The issue of “real” dimensions versus “nominal” dimensions often comes up. Finished dimensions are obtained after removing the roughness from the top and bottom of the boards. Lumber widths and thicknesses aren’t always what they seem to be. As a result, lumber usually called 1x4 is actually 3/4 of an inch thick and a good deal less than four inches wide. Fine hardwoods used in architectural woodwork are not purchased in the same way as “lumber yard” boards. Woodworkers buy hardwoods in random widths and random lengths, selecting from the bundle those boards which make the best use of the natural resource while meeting the grade of work specified. Gluing for thickness is always a good idea when very thick members are required. Properly sawn and selected glue-ups are usually more stable than full size pieces of the same dimension. Gluing for width is more common than gluing for thickness. Modern adhesives, combined with a careful selection for grain and color, makes edge-glued lumber a good choice. Edge gluing limits waste, reduces cost, and is the environmentally sound use of the natural resource. The matching requirements for glued members are as follows: Grade I—well matched for color and grain Grade II—compatible for color and grain Grade III—no matching required As noted above, the terms “well matched for color and grain” and “compatible for color and grain” are defined in the Glossary on page 29 of the Architectural Woodwork Quality Standards Illustrated, 8th Edition. Tables 100-T-4 and 100-T-5, pages 28-29, provide natural characteristics and limits of natural characteristics permitted for the lumber grades. These tables are for your reference after you work through the fabrication sections. When you see the lumber grade referenced, you can refer to these tables to see what natural characteristics and variations you might expect. Remember that judgment on the appearance of the wood only applies to material after fabrication. A woodworker may buy a low grade of lumber, but spend the labor and time to select and cut for compliance. For species not listed in the tables, and there are many in use today, the allowable natural characteristics are as agreed between buyer and seller. I Spring 2008
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