On new wood vs. old wood:
> << It would be great to get some real wood technologists to jump into the
> middle of this. >>

This morning I talked with Joe Lofersky, wood scientist at Virginia U.,
presenter at our APT exterior wood preservation workshop in Banff last fall.
I checked with him to clarify a few details about what we learned. He sez:

- we assume here "new wood" means modern cut, 2nd, 3rd, 4th....growth north
American species
- sap wood, starches and sugars are all much higher in new wood, and
extractives are much lower
- more sap wood means more of the building part is susceptible to powder
post beetles
- more starches and sugars means the wood is more desirable to pp beetles,
but ants and termites could care less. Molds, mildews also grow better on
new wood with higher starches and sugars, they can cause staining and paint
failure though they do not weaken the wood. (Bryan's point about molds &
mill dew eroding the wood surface and causing paint failure fits with my
experience too.)
- ants like softer wood, most new wood *is* less dense, damp or wet wood is
"softer" and more desirable to ants. Fewer growth rings per inch in fast
growing new wood (in softwoods) means it is less dense.
- cubic brown rot could care less about starches & sugars because it grows
on the cellulose, but may be seen more on new wood because the wood has
higher moisture content due to these other agents of wood destruction.

Since I first had a discussion with Bryan about the starches & sugars in new
wood a few years ago I have seen 4 cases where new wood was placed next to
old and the new wood, especially the sap wood, was preferentially attacked
by most or all of the agents listed above. It is amazing how much exterior
woodwork is blowing off many of the high end condos built in the 1980s boom,
much of it specified as premium grade wood, but mostly sap wood. (by
"blowing off" I mean blown off by breeze, not by dynamite.)

We always use old wood when we can in our window (and other) repairs, though
some unknowledgable architects have sometimes specified and lobbied against
using second hand wood for fear of decay organisms in the wood. These fears
may be justified when tradespeople do not know how to detect fungi with
microscopes and stains, or how to treat the wood (borates, water repellents,
effective details, etc.).


John Leeke, Preservation Consultant

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