Thanks, Brooke. I read a discussion about One Time Wood on one of the forums here. It seems to be some sort of a plastic product, and it is also pigmented; I need something that is clear. I would love to use something that lasts for 7 years, but...The discussion is interesting, anyway, with users really liking it (though not having had it in use for seven years as yet) and others who haven't used it with some rather negative opinions! cuestatoble - Thank you also for the info about the copper naphthenate. I think I will probably use it on the bottom of my posts of my shade garden structure. They do touch the soil and I don't want them to rot out! Holly Here is a link that might be useful: One Time Wood discussion

Thanks for the input. The interior opening at the top of the column is 3 3/4". I guess I would be more comfortable using the wood posts rather than trying to fill pvc pipe with concrete. I didn't really investigate regular wood columns which they also carry at the store. I figured the fiberglass would hold paint better and last longer. I may go back and read the brochure for the wood columns to see if they might be easier to install. It's just frustrating when you take a plan book to the store to clearly show them your project and even then the employees really don't seem to have a clue about how to install their merchandise. BTW, I tried to attach a photo of the type of arbor I'm trying to build to my original question, but I don't know how to insert photos into a message.

I recommend against using PT to build your Pergola. PT is pine afterall, treated to resist rot. It tends to warp in the sun. Cedar is the long-time standard for outdoor construction but new species have been introduced. I do not know their relative cost. Speak with a quality lumber yard, not a Home Center, for their recommendations. If the lumber cost is more than this years budget will permit, consider a multi-year build. Don't skimp as you will never regret doing it right the first time. Your Pergola will be considerably larger than ours. You may want to use 4x or double-up the lumber for your spans. Our Pergola measures 8 x 12 on centers with a 2' overhang at the corners. The very top is vinyl lattice. I've linked photos taken while ours was being assembled and the one below is totally finished and ready to enjoy. Best of luck building yours. Here is a link that might be useful: Our Pergola

Ipe is an excellent choice for a pergola. It is heavy and dense wood, but very strong at the same time. 1x4 Ipe is stronger than 2x6 Redwood or Cedar. You can keep the weight down by going smaller. There are many South American ironwoods available, but Garapa, Cumaru, and Massaranduba are less dimensionally stable than Ipe. The long spans of a pergola will be way more subject to movement than a deck fastened to joists on 16" I think Ipe is your best choice. Ipe is so dense that it can be tempermental with taking a finish. The untinted paint base is a great clear finish for solid wood exterior doors and millwork. However, do not put it on Ipe. Finishes that dry to a film will fail on Ipe. Ipe needs a penetrating finish. TWP and Woodrich seem to get the best reviews from professionals and no horror stories from DIY'ers. There is plenty of advice over on the deck forum.