Choosing and Using Redwood | |
Redwood has natural qualities that make it an excellent choice for either exterior or interior projects. The close grain and natural resistance to damage from either decay or insects means that projects built of redwood will hold their value and age beautifully. Redwood also takes and holds a protective finish --paint or stain -- better than many other wood species. Use redwood for siding, decks, fences, or other exterior applications where both beauty and durability are required. Although redwood can seem a bit expensive, the consumer can stay within the budget by being sure to specify the correct material choice for the job. For example, only the wood that will be in ground contact needs to be the most expensive heart lumber: cheaper grades can be used for above-ground applications. Specifications should include: use, grade, grain, seasoning, size, and texture information. Your lumber dealer can help you choose the best grades for each particular part of your project. There are more than 30 grades of redwood lumber. A primary factor in grading redwood is appearance and color. Reddish-brown heartwood contains extractives that protect it against decay and insect attack. The lighter, cream-colored sapwood that grows in the outer layer of the trees does not have the natural protective characteristics of heartwood. Other grades are determined by the size and number of knots and the presence of stains or manufacturing defects. The grades are: --Architectural grades: Clear All Heart, Clear, and B Grade are all kiln-dried for the premium interior or exterior applications. These architectural grades are the choice grades for siding, paneling, trim, and cabinetry. --Garden Grades: Construction Heart, Construction Common, Merchantable Heart, and Merchantable grades may be specified for use where knots or color variations are not important. Decks, fences, and other garden projects are typical uses for the garden grades. For projects where the wood will be in or near ground contact such as posts or patio grids, use one of the heartwood grades such as Clear All Heart, Select Heart, Construction Heart or Merchantable Heart. For projects where the wood will not be in ground contact, one of the less expensive sapwood-containing grades will serve as well, and at the same time will help you stay within the budget. These grades are Clear, B Grade, Select, Construction Common, or Merchantable. Characteristics of Redwood A very important characteristic of redwood is its stability, or resistance to shrinking. In fact, tests by the U.S. Forest Products show that redwood has the least volumetric shrinkage of any commercial American wood. The tests showed that from its green condition to a 10 percent moisture content, redwood shrinks only 1.7 percent across the vertical grain and only 3.3 percent across the flat grain. This resistance to shrinkage plays an important role in the quality of the finished project. As we have mentioned earlier, lumber that shrinks excessively will cause your project to have loose joints, popping nails or other fasteners, structural sagging, and premature failure. We have already talked about redwood's durability, its natural resistance to decay and to insect infestation. Natural extractives in the heartwood provide high resistance to termite attack and make redwood one of only two untreated woods approved for use as foundation plates or "mudsills" by the Uniform Building Code. To have superior gluing qualities, the strength of the glued joint should be equal to the strength of the wood itself. Redwoods perform well with glues and adhesives. Also, the texture and grain patterns of redwood make it easy to work with a plane, joiner, or router. Other positive characteristics of redwood include a good strength-to-weight ratio: redwood is one of the lightest softwoods used for structural purposes. It has good nail-holding power and, because it has no volatile resins or oils, good fire resistance. For further information on redwood, contact the California Redwood Association at (415) 382-0662. Written by Gary Branson Reprinted with permission. Copyright HouseNet, Inc. |