I would use a long drying oil based exterior primer. Oil or latex primers can both be topcoated with oil or latex paints.

thx paint guy - actually a local paint store guy just told me something similar - "long drying" - why would something that takes a long time to dry be preferable to something like the zinsser oil base which driesin 2 hrs?

Im not questioning the advice, its just the 3-yr old in me always has to know the "whys" about everything. How long is "long" - imagine it would need to be good and dry before painting w/ latex.

Thx - once I get the primer up can I consider it protection against the rain? This whole business of putting up tarps & taking them down & putting them back up - repeated ad nauseum, is starting to get to me!

Im still waiting for my epoxy repairs to dry - still a little sticky. Should those be completely hardened/cured before primer?

Alkyds cure by the process of oxidation. A long dry oil primer, in the process of production, has not reacted nearly as much as a fast dry. Once applied to a surface a long dry's life span will be longer. A fast dry will become brittle and fail quicker.

I've heard the same about penetration. But really though, I don't think paint in general penetrates that deeply into wood for there to be a difference between long and short oils. I could, and may be wrong.

There are also different grades of long oil primers. Under identical circumstances, one manufacturer's long oil primer may be ready for topcoat in 24 hours, and another company's slow dry primer may not be ready to topcoat for 7 days.

Whats your take Paintguy and samah re: acrylic vs. oil? I just looked at some other paint jobs with epoxy repair I did on window trim about 5 yrs ago - topcoated only with Zinnsser permawhite. Still good! No signs of peeling whatsoever.

I thought I would use same paint again on the porch, but use primer under it because I remember it took like 5 -7 coats of the permawhite (its thin) to cover up the wood color. But heck maybe Ill just do the same thing again . The difference is though that I probably used more liquid wood on the window trim (a two part liquid epoxy wood hardener) whereas with the porch I went a little lighter on that - since there was so much more wood and a lot of it was still good, not soft.

You should still prime it first.

Yea, priming is just your best option because it may help solve problems that you don't even know about.

Before you prime it, apply a coat of something they call blopentine to the areas of bare wood - a 50-50 mixture of boiled linseed oil and turpentine. Google blopentine or ask about it on the Old House forum.