Red pine ( Pinus resinosa ), also called Norway pine, is found in the northern tier of states, east of the Mississippi River, and into eastern Canada. For many years, it was the choice of people planting trees in the cut-over white pine forests of the North. In some ways, the wood is better than the white pine it replaced. Today there are a lot of 50-year-old trees that are mature and ready to cut.
Although the annual rings are quite pronounced, making painting difficult, this strong and stiff wood has high potential for many non-paint uses. Its moderate natural decay resistance makes it attractive for above ground outside uses.
Some stands of red pine are prone to developing compression wood in the tree during early growth of the tree. This wood is weak and shrinks lengthwise causing warp.
The mature tree (75 years) is about 80 feet tall and up to 3 feet in diameter. When forest grown, this mature tree will produce a large amount of clear lumber. Because the dead lower branches remain attached to the tree for many years, the wood will grow around these knots and encompass them. The lumber that includes these knots will have a black ring around the outside of the knots where the bark is attached. Hence the name "black knots." A black knot is held in place by geometry and resin. During drying, the resin can melt and the knot shrink enough so that these black knots can loosen and can fall out, leaving a knot hole. (If the branch were alive when the wood grew around it, then this is called a red knot. Red knots are an integral part of the wood, so they do not loosen.)
Processing suggestions and characteristics
Density. Red pine averages about 33 pounds per cubic foot at 8 percent MC. This is roughly 20 percent heavier than ponderosa pine and 33 percent heavier than white pine, and about 10 percent lighter than Southern pine. Some zones of compression wood may be higher in density.
Drying. Red pine is an easy-drying species, but the wood near the center of the log (sometimes called juvenile wood and extended for about 15 rings or years from the center) often shrinks unevenly lengthwise, creating side bend and bow during drying. Some blue stain can develop in warm weather if drying is not aggressive enough or if logs or green lumber are stored rather than processed immediately. Shrinkage in drying is 6 percent.
Final moisture contents for red should be between 8.0 to 9.5 percent MC, which is higher than most hardwood lumber. Excessively dry wood will require increased glue spread to avoid a starved joint and will likely develop torn grain, planer splits and brittleness when machining. Boards with MCs much over 9.5 percent MC will likely shrink as they dry in use and may develop some warp or shrinkage defects.
Gluing and machining. Red pine machines very well if not over-dried, although some grain tearout may occur around knots.
Red pine is easy to glue. The softness means that the wood is somewhat forgiving, if gluing conditions are not quite perfect. At times, the resin can interfere with gluing, so fresh, clean surfaces are required. PUR adhesives may be required.
Stability. Red pine is subject to modest size changes when the MC changes - about 1 percent size change running across the grain parallel to the rings (tangentially) for each 4 percent MC change, and about 1 percent size change across the rings (radially) for each 8 percent MC change. Compression wood and juvenile wood do cause excessive movement when the MC changes.
Strength. Red pine is medium in strength and stiffness. The bending strength (MOR) averages 11,000 psi. Hardness averages 560 pounds. Stiffness (MOE) averages 1.63 million psi. These are considerably higher than Ponderosa and white pine; they are close to radiata pine values.
Color and grain. The sapwood is white, while the heartwood is red to reddish brown. The grain is straight with a medium texture. The growth rings have quite high color and density contrast. This makes durable painting difficult. The wood does have a slight pleasant "pine" odor with an oily resinous feel.
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