No wood is in the same class of durability as metal, stone, or concrete.
There are also issues of stability, wood will certainly swell and contract,
and a precision dial will be compromised.  The harder, closed-grained woods
tend to move less than the softer.  Contact points between a wood surface
and metal, plastic, or concrete will often stain and be the first point of
rot.  If the area is frequented by dogs or cats, if they 'mark' it in their
standard fashion, that will quickly decompose any wood.
Paint and varnish require maintenance every few years and often cause
problems, by allowing penetration through cracks and then trapping moisture
in the wood.  Boat trim would be left unvarnished if ultraviolet light
weren't so destructive. Since paint covers the attractive qualities of
wood, a painted dial might as well be made of a more durable substance.
Durability is greatly reduced by freeze/thaw cycles, continual high
moisture, and strong sun (keep the dial in the shade if durability is
important).  Teak will develop very small cracks but is fairly stable and
can last several decades.  Purpleheart will quickly turn brown but can last
almost as long.  Osage Orange is durable.  Port Orford Cedar, Redwood, &
Alaska Yellow Cedar are three rot-resistant softwoods in order of
durability, that can probably last a couple of decades, but are more prone
to movement than most hardwoods.  However, there are no generic
recommendations for wood, the climate of the location must be considered.
Cupping is minimized by vertical grain sawing, but you usually don't have a
choice in the exotic woods..
Wood is my favorite material but I am also fond of the results of my
labors, and I personally don't use wood for anything placed outdoors that
is more elaborate than a picnic table.    --Peter

>I would be interested in getting a variety of opinion and/or
>experiences relating to the use of wood for outdoor, all-weather
>sundials.

_______________________________________
Peter Abrahams   [EMAIL PROTECTED]

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