Which is best choice? Contractor says pressure treated pine does not hold paint because it might still be wet. He prefers primed and painted yellow pine. This is for a rental. On my home I live in, I have seen the untreated Yellow Pine (fascia) fail in <8 years even though it was primed both sides with Kilz. 19 years ago I had treated pine 1x4 trim installed and painted and still is good. Oil base primer will be used regardless. Is there a pressure treated 1x4 spec. or brand that is more dry & paint friendly? This is Houston so high heat & humidity and lots of rain.
I think there is some confusion going on, pressure treated lumber for ground contact and yard / deck use is a completely different animal than the pressure treated radiata pine product that is used for trim, fascia, and barge rafters. This material is kiln dried and as a contractor since 1989 and a carpenter since 1978 the pressure treated resawn pine is used 80% of the time and is sold in all lumber yards including home depot and lowes. It is expensive but comes with a heavy prime that seems to be infused into the wood, no knots, and is rot and mildew resistant, very straight and does not shrink, split or warp. All the large lumber companies have their own brand name for this product. Its probably not used on some lower end tract homes because of its cost, but in the long run it is more stable than the clear resawn cedar and redwood we used to be able to use.(even in the 70's almost clear redwood 2x8's were extremely expensive, and they were usually somewhat wet so they would change a bit over time).
The pressure treated material will need to set unpainted for about 6 months. Not only is it excessively wet from the treatment process, it will leach some of the treatment through the surface for a time. In essence giving no surface the primer or paint to grip on. There may be water based stains that will work, but no opaque paints, especially oil based.
The yellow pine will be your best choice between the 2. If it is affordable there are other choices too. Yellow pine needs to be fastened on place really securely. If it wants to move it will. You will need to prime it on all sides before cutting, let it dry, and prime the cuts before securing it in place. This will keep the material a little more stable, less prone to rotting in exposed conditions.
I don't think pressure treated wood should ever be painted. It just never works in the long run, no matter how long it stands in the open unfinished. PT wood has high amounts of metal and mineral salts in it that will always retain moisture from the surrounding air. It will always be wetter and change size more dramatically through wetting and drying cycles than plain-old untreated wood will be.
Just get the straightest grained knot free untreated 1x boards that you can find and afford, paint them, and use those. More important for the life of wood trim than the specific material it is made of and the paint put over it is the design and geometry of the trim work and the quality of its installation. Is the trim drained properly? Can it dry out quickly after rain? Is it nailed properly? Is it fitted nice and tightly? These details matter the most. I can elaborate on them if you'd like. I've worked on many old homes with 100% wood exteriors and I've seen what works and what doesn't.