Hi Jim. You write,
I'll use 4x4" treated posts and 2x4 treated cross
braces, but the table tops are going to be that
plastic lumber. With luck, I'll never have to build
another set of tables!
Trust in plastic lumber's useful life might be ill-advised. A professional
architectural firm recently provided a friend with figures to project
reserves for her community's replacement of mixed fencing-- the treated wood
fencing (at less than half the running cost of substantial plastic fencing
of identical height) had a 20-year life whereas the plastic fencing was
projected to last 25 years. What are "lifetime" warranties worth for vinyl
clad windows and vinyl siding-- they are not "for the ages."

Of course, your tabletops will hopefully be graced always with shade from
pots and bonsai, which could extend sun damage. Redwood or old cypress, if
maintained modestly with a pigmented stain, would outlast 25 years even on a
watered bench. The secret is perhaps in sealing holes (e.g. closely
fitting bolts or pegs) to maintain wood integrity at joint connections.
Rigidity of the plastic & choice of connectors (nail gun?) probably affects
its life.

Best wishes,
Chris... C. Cochrane, , Richmond VA USA

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