If you’re shopping at lumberyards or home centers for posts, decking or almost any kind of lumber, prepare to hunt through the pile. Take what you need off the top or accept a delivery without checking and you’ll probably be in for some extra work (and extra waste) dealing with the warps, twists, splits and other defects. Lumber just isn’t as good as it used to be.
One reason: an increasing amount now comes from smaller, younger, faster-growing trees that aren’t as dense or as strong as the dwindling supply of larger, older, slower-growing trees. In fact, a survey of builders by the Center for International Trade in Forest Products found that the use of traditional solid lumber has declined substantially since 1995. At the lumberyard and home center, you’ll wade through 2-by-4s, 2-by-10s and other traditional lumber with several possible problems.
Heavyweights. To be stable–to stay where it’s nailed without shifting–construction grades commonly used for framing contain less than 20 percent moisture. You should see a grade stamp that says “19% MC” (the percent of moisture content). But some timbers carrying the right number also carry excess moisture and feel much heavier than same-size boards. That’s usually because they’re loaded with water.
This lumber may be straight and true to start with. But as water-laden wood dries out in the walls of a house, excess moisture evaporates and leaves spaces between the strands of wood grain. As the grain shifts to fill the gaps, lumber shrinks and twists. It’s often a gradual process but eventually powerful enough to pop nails, raise seams between drywall panels and open trim joints–even if the framing is set in the right position initially and properly nailed. You could check for heavyweights with a moisture meter. But if sifting through lumber by hand, the extra weight is a giveaway.
Cupped lumber. Cupping is a twist across the grain that creates a concave surface or trough. Minor cupping is not a big issue on framing, though it does distort nailing surfaces somewhat. It is a problem on decking where the cup shape can trap water on a 2-by-4 and even more so on a 2-by-6.
You can spot cupping at the end of a board where one side is concave and the other convex. If you have to use a deck board with a slight cup, install it with the cupped surface down so the board sheds water instead of collecting it.
Warped lumber. Warping is a twist (or two or three) with the grain that can bow a 2-by-4 into an unusable shape. You can check for bowing by sighting along the length of a board or by lying it down on a flat surface like the store’s concrete floor, first on edge, then on its side.
If there are obvious gaps, it will be difficult to force the warped stud, joist or rafter into proper position. There are crooks, crowns, checks and other imperfections that don’t usually cause problems on beefy timbers used for framing and decking. But noticeable warping or twisting is another matter. Even if you can pry and nail one of these twisters in position, it’s not likely to stay there for long.
Splits, wanes and knots. Splits through the full thickness, usually at the ends of timbers, make structural lumber unusable.
Wanes often look as though a section has already split off along one edge. This largely cosmetic defect stems from cutting lumber too close to the edge of a tree, taking a slab of bark. When the bark falls away, the board comes up with three square corners instead of four. Small wanes are no problem. But large ones can undermine support for drywall or paneling.
Knots are cross sections of branches that were enveloped by the growing tree. Small knots are no problem, including loose knots that pop out during handling. Large knots–through most of a 2-by-4, for example–create a weak spot.