Pressure treated would be a good solution - but if you don't like it, regular 2Xs could serve you well under the right circumstances. A good shellac or spar varnish could go a long way. The major obstacle you face is the feet - will the bench sit on open to weather ground? or will it sit on a porch (open or roof)? The end grain from most lumbers will absorb moister and that will be your major challenge.
I had wooden pine planters on my front porch that got drenched with water everyday. They lasted about 12 years the tops are what rotted - they were always wet...
When working with pt wood, I always use a cheap contractor's blade... been using the same one for about 14 years. It's never been sharpened but I've put it into a vise and scraped the gunk off and around the teeth many times. PT lumber is wet and is hard on the blades. My good expensive blades have never touched it.
If you use pt - you don't need to finish it. If you want to finish pt - let it dry, sand it and finish it. As for gluing pt - the longer it dries, the better it will be... You could experiment a bit with the wet stuff if you use a "construction" adhesive like "Liquid Nails" or "Loc-Tite" The stuff will expand and you will need to be watching it and scraping it as it expands. I prefer the "Loc-Tite" product - just my preference.
Trying to keep up with you... use non pt with a spar varnish - just be concerned about the feet
So if I go non-pressure-treated. What if I were to use some type of metal cup type thing to go over the bottom of the feet? This way the metal will be in contact with the ground I could use copper or aluminum
Poly is for interior applications only. Spar is for external. Use a waterproof glue such as TB III and use several coats of Spar and be sure EVERYTHING is coated well. Your finish does nothing if water can get under it.
Personally, if I were making a bench for outside and using construction grade lumber Id use PT. In the end it will all look the same after the sun does its thing.
I would suggest going with redwood also but if you want to use pine you don't have to treat the whole thing as long as you are using a good uv outdoor finish. Just treat the areas were the wood will be touching the ground with Wolman or alike wood treatment.
I also like to use a polyurethane glue that is moisture activated like Gorilla Glue but T-lll works well too.
I don't care for the PT wood because of the chemicals used and sometimes reactions it causes to some people when they make contact.
Just try to seal and finish it well and it will last for many many years.
Your weather extremes are probably like ours between summer & winter, fog/rain and sunshine.
Outdoor furniture, log furniture and serious log homes are usually finished with Sikkens Cetol.
Nothing else is as weatherproof. Expensive, but cheaper than refinishing and doing it twice.
The humble abode on the home page at Magard Log Home Building Tools is a nice example.
Chainsaw carvings (3' - 12') get either Cetol or spar varnish if they are even a little bit sheltered.
End grain on table/chair/bench feet: Out on the lawn, most people use small slabs of slate, Lots on the roadsides for the picking. The deal is to keep the foot-ends from being perpetually soggy.
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