Dan:

Much of the following grows out of my own trades work and long-term
side-by-side comparitive testing in the field over the past 30 years, some
comes out of Protecting Exterior Wood, the APTI post-conference workshop at
Banff a few years back.

Use a decay resistant wood. Any of the affore-mentioned species would be
good. My
first choice has most often been Mahogany in recent years. I would leave
white oak and redwood at the end of the list as not particularly machineable
and lower in paint-holding ability. However, specifying a species of wood
will get you only a small part of the way toward extending the service life,
since a "good" piece of Eastern White Pine can last much longer that a "bad"
piece of Maghogany. In any case the experienced, knowledgable and effective
woodworker will cream the stack to select best planks, or order 20-40% more
than needed and not use the worst wood; selection based on rejecting the
planks or cuts of wood that will fail in service, keeping in mind that decay
is only one of the many failure modes of exterior wood assemblies.

If your goal is to extend the service life you will do well to pay
significant attention to these additional issues:

"keep the wood dry and allow for movement:

- Provide a stable foundation or sub-structure
- Select appropriate materials
- Ventilate hollow spaces
- Drain horizontal surface
- Protect individual parts
- Exclude water at joints between parts"

-- excerpt from "Exterior Woodwork Details," Practical Restoration Reports
series

Decay: treat all locations and parts likely to decay with borates

End-grain: seal with a penetrating resin that does not taste like food to
bugs and plants, I have consistent good results with epoxy consolidant.

Assembly and coatings procedure: cut, fit, trim, assemble "dry & bare";
disassemble; treat all end-grain; treat all surfaces of all parts with
paintable water repellant, prime all surfaces, paint all surfaces with one
top-coat of paint (except where sealant will be used), assemble parts, seal
or flash upper joints 'water-shed joints', leave lower 'draining joints'
open, apply two more coats of paint. (Of course, there will be exceptions to
this treatment sechedule in a structure as complex as a curved stairway, but
it does apply well to most exterior woodwork assemblies.)

Organization: As part of the original contract specify a followup after one
or two years to "touch up" "pre-maturely" failing paint spots, joint seals,
wood parts, attachements, etc.  No matter what species of wood is used, or
how meticulously the original work is done there will be at least a few
minor failures that need attention. If these are caught soon after the
original work, they will not develop into the major failure points that
result in significantly costly repairs in 10 to 15 years.

Maintenance: Schedule and implement routine paint and sealant maintenance at
least once a year on wearing surfaces such as treads and decks, every 2
years on everything else.

Spirit: Walk across the park at least once every 5 years and assend the
stairway to enjoy the fine curves and determine how they relate to the pulse
of the universe.

John
by hammer and hand great works do stand
by pen and thought best words are wrought

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