Types of Preservatives
Lumber is a general term for all types of wood products cut from a log into all sizes and shapes, which may be treated with preservatives or not. There are two types of lumber: softwoods and hardwoods. Softwood lumber comes from conifer trees like pine, fir, spruce, and cedar. They can be easily dented with just your fingernail.
Hardwood lumber comes from deciduous trees, which have broad leaves that fall off in the cold months. The most common trees you’ll see hardwood lumber come from are oak, maple, walnut, hickory, and mahogany. As you can gather from the name, most hardwoods are harder than softwoods with the exception of balsa wood.
Softwood — while not soft — describes wood product milled from evergreen conifer trees such as pine, fir and hemlock. These trees keep their needles year-round. Softwood has a broad range of uses, with 80 percent of construction materials created from Softwood, including window frames, interior doors, medium-density fiberboard, and studs. Douglas Fir, Hemlock, Pine and Cedar are the main sources for building materials. Softwood trees have a faster growth rate. The grain of softwoods is less dense than in hardwoods.
Hardwood is the term for wood milled from deciduous trees—those that shed their leaves. Walnut, Mahogany, Oak, Maple, Alder, Hickory and Teak are the most popular. These hardwoods are more expensive and are mainly used for furniture, cabinetry, flooring, and decks. The grain in hardwoods is denser than in softwoods.
Pressure Treated: Used on the exterior of the home. To reduce deterioration of wood products due to insect, or other micro-organism, and mold/decay fungi attack, wood exposed to moisture is treated with chemicals. By forcing preservatives deeply into the wood, organisms cannot use the wood fibers as food.
Dimensional lumber: while named the “actual” or “nominal” size, dimensional lumber will be smaller in width and depth due to shrinkage from drying and planing. Cut to actual size at the mill, the wood then may be dried and planed, reducing the nominal size to the dimensional. Length is actual. For example: 2 X 4 reduces to 1-1/2” to 3-1/2” in width and depth. An 8-foot 2X4 will measure 8 feet long, but 1-1/2” by 3-1/2”.
Green lumber refers to milled wood products with a moisture content of 19 percent or greater.
Dry lumber has been dried or seasoned to less than 19 percent moisture content.
Kiln dried means it was seasoned or heated in a chamber to reduce moisture content.
Heat-treated refers to wood placed in a closed chamber and heated to a core temperature of 56-degrees C for 30 minutes, which may or may not reduce the moisture content.
Rough sawn may show the edges from milling and will not be finished with sanding or planning.
Dressed or Planed has a smooth finish produced by mechanically removing the rough surface.
Softwood lumber is classified by government standards as Yard, Structural, and Factory and Shop Lumber, which is used in smaller pieces for remanufacturing, such as door rails and stiles, or in wood ladders.
Yard refers to lumber used in general construction, such as boards, laths, and wood siding. The lumber is graded visually:
• C Select is almost free of all defects; used for cabinets and shelving
• D Select is almost free of defects but may have small knots less than the size of a dime
• 1 Common contains knots that are small, tight and won’t fall out, such as pine
• 2 Common contains slightly larger knots; may be used for shelving.
• 3 Common contains larger knots and is suitable for fencing or crates.
Structural Lumber is used in framing buildings as posts, beams, studs, rafters, joists sill plates and wall plates. The size chosen will be determined by its use and strength or bendability. 2X4; 2X6; 2X8; 2X10; 2X12; 4X4; 4X6; 4X8; 6X6; and 8X8 are the sizes produced as dimensional lumber.
• Machine grading measures stiffness or density to provide information the builder needs to construct appropriately. Moisture content and species are also noted as well as the mill producing the lumber. Species is included in the grading. The following are grades for Western Wood Products and Southern Yellow Pine, although SYP are graded for the first three only.
• Structural Light Framing (SFL) is 2” to 4” thick; 2” to 4” wide grades Select Structural, No. 1, No. 2 No. 3 used in structural applications where highest design values are needed in light framing sizes.
• Light Framing (LF) is 2” to 4” thick, 2” to 4” wide grades Construction, Standard, Utility used where high strength values are not required, such as wall framing, plates, sills, cripples, blocking, etc.
• Stud2” to 4” thick; 2” and wider graded Stud is an all-purpose grade for studs including bearing walls.
• Structural Joists and Planks (J&P) are graded as Select Structural, No. 1, No. 2 and No.3.
• Beams and Stringers are 5” and thicker, width more than 2” greater than thickness are graded Dense Select Structural, Dense No.1 and No. 2 (Doug Fir or Doug Fir-Larch only); Select Structural, No. 1 and No.2 used for beams and stringers when sizes are larger than 4” nominal thicknesses are required.
• Post and Timbers 5” X 5” and larger; width not more than 2” greater than thickness Dense Select Structural, Dense No.1 and No. 2 (Doug Fir or Doug Fir-Larch only); Select Structural, No. 1 and No.2 are used for vertically loaded applications where sizes larger than 4” nominal thickness are required.
• Structural Decking 2” to 4” thick, 4” to 12” wide Selected Decking used where appearance of the best face is important; 2” to 4” thick, 4” to 12” wide. Commercial Decking is used when appearance is not of primary importance.
• Softwood Boards are cut less than 2” thick and 5” deep in various lengths used for moulding, shelving and woodworking projects.
Timbers are milled 5” thick or greater and used as beams, stringers, posts, caps, sills, girders, or purlins.
Treated lumber is milled to dimensional standards for use in outdoor projects such as decks, sheds, etc. Decking is milled with curved edges for use as deck flooring and railing. Treated with preservatives described above, deck boards are pine milled to about 1-inch thick by 5-1/2 inches. Some deck boards may be slightly thicker.
Hardwood does not have standards like Softwoods, but hardwood is cut in ¼’ thicknesses, ranging from 1/2” to 4”in various lengths. Mainly used for cabinetry, moulding, shelving, woodworking projects, and crafts.
Grades for Hardwood:
• FAS (First and Seconds) highest rating, with 83.3 percent usable; minimum board 6” X 8’.
• F1F (First One Face) better face will be FAS, the poor face will have minor defects (No. 1 Com) Minimum board 6” X 8’
• Select: better face will be FAS, the poor face will have minor defects (No. 1 Com). Minimum board 4” X 6’
• 1 Common: Have minor defects ; 66.66 usable material; Minimum board 3” X 4’
• 2A Common: Have some defects; 50 percent usable material; Minimum board 3” X 4’
• 3A Common: Have many defects; 33.3 percent usable material; Minimum board 3” X 4’
Waterborne, copper based preservatives prevent termite attack and fungal decay. Copper Azole (CA) and Alkaline Copper Quat (ACQ) are used in exterior residential, as well as commercial and agricultural construction.
Chromated Copper Arsenate (CCA) is no longer permitted for residential use by the Environmental Protection Agency. It may be found used on Utility Poles, Highway Construction, etc.Micronized Copper Azole (MCA) contains micronized copper and biocides, providing less copper leaching from the material. For use in outdoor and landscaping projects.
Borate (SBX) is the most commonly used of the Carbon Based preservatives (PT1 and EL2) to treat wood used in residential construction, except where the wood meets the ground. Used for sill plates, roofing trusses, joists, etc.
Creosote is one of the oldest preservatives and used for severe environmental situations, such as railroad ties, commercial, industrial and marine installations. Not for use in residential applications due to the odor and oily appearance.
Oilborne preservatives such as Penta, Oxine Copper and Copper Naphthenate are applied for industrial applications.
Bow - Warp from end to end
Cup - Warp from side to side
Crook - Warp at one end of the board
Twist - Combination of bow, cup, and crook in a board
Knothole - Hole left in the board when a knot falls out
Split - Crack completely through the board thickness
Check - Crack on one side
Shake - Crack following the grain
Wane - Edge missing on one side