In article <86afizbxsy.fsf at coulee.tdb.com>,
Russell Senior <seniorr at teleport.com> wrote:
> There is a good example of this at the Redwood State Park along the
> Avenue of the Giants in California. In the interpretive center they
> show the difference in ring pitch between an `old-growth' and a
> second-growth. The ratio is about 10 to 1. I do not know what the
> consequences are for the mechanical characteristics of the resulting
> lumber, but the difference is certainly obvious to look at.
> Closer to home (mine at least), next time you are hiking in the
> Mt. Hood Nat'l Forest, check out the rings in the blown down timber
> crossing the trail. An average, sort of piddly looking 24-inch
> diameter log is probably about 300 years old.
> So, what _are_ the consequences on the mechanical properties of the
> wood? You may get the same volume in a shorter period of time, but
> what about its strength?
Dense grained heartwood is prized for woodworking, cabinetry and such.
This doesn't make much difference to west coast conifers, since they are
rarely used for cabinetry anyway. Generally they are not hard enough
and are too porous to take a fine finish. However, you may have seen
some of the old oil finish pine floors that were common around the turn
of the century. Board floors of dense old-growth pine heartwood are
practically indestructible. Some of them have been in high traffic
commercial use for 100 years and are still servicable floors.
There's a saying, "Tough as an old pine knot." I once saw a logger bend
the edge on his axe trying to trim a pine knot off the side of a log.
Both veneer and lumber prefer the tighter grained wood. A #1 peeler
doug fir is required to have 8 rings/inch, and a #3 peeler is required
to have 6 rings/inch. I've seen doug fir with 3 rings/inch, and maybe
even 2 rings/inch.
The faster growing wood is still suitable for construction. It's very
nearly as strong as the denser wood, under most applications. The looser
grain is more flexible, so horizontal supports are bouncier and more
subject to longitudinal stresses.
For floor joists and such, the question is pretty much academic any more
anyway. Rising lumber prices have driven solid wood horizontal supports
off the market. They've been replaced by manufactured composite members like
TJ-I's that have more glue in them than wood. Veneer plywood has in many
cases been replaced by oriented strand board. In truth, the new high-
tech composites are stronger and lighter than the old solid wood structural
members. They are not necessarily cheaper, because they require fabrication
and some non-renewable raw materials.
Large wooden beams have completely vanished from the market. If you want one,
you have to contact a mill and have it special cut for you. They have been
replaced by glue-lams, wooden beams built up by glueing and laminating many
pieces of smaller wood. Like any composite material, this limits the size
of defects to a small portion of the member size. They are stronger and
more reliable than solid wood.
Most of this technology has been developed because the old wood supply was
inadequate to meet demand. It allows wood cut from smaller trees to
serve in heavy applications.