Peabody wrote:
I have some large fir beams that stick out from under the roof line,
and they have deteriorated. The beams were last painted with
exterior latex paint, which didn't work very well in keeping the
moisture out. So I'm going to be digging out the rotted parts and
putting in filler.

But some portions of the beams are still ok, for now. Do I have to
remove all of the latex paint, and then put on an oil-based
primer/sealer in order to get good protection? Or would it be
possible to leave the good parts as they are, but cover them as well
as the repaired portions with a latex primer? I see that Valspar has
a latex primer, and perhaps there are others that would work.

It would be very difficult to remove all of the old latex. The beams
are quite rough, with lots of raw wood texture, and I'm concerned
that even with a chemical stripper I wouldn't get all of it out. And
you know, if possible I'd like to not make a career of this.

I should say that in the end the beams will be painted with the same
exterior latex paint I'll use for the trim. So I guess I was just
hoping I could find a way to stay with latex all the way through, and
avoid issues of what I can paint over what. But I'm just not sure
that will work for a fir beam sticking out in the rain. I have made
metal caps for the beams from gutter stock, and that may help some.

I would appreciate any suggestions on how to proceed.

Use oil based primer. It'll stick to latex.