Oil base primer or laytex with laytex
The subject is exterior paint. I have always heard that you want the primer to really soak in good and bond to the wood. As such, I have always thought the best combination would be an oil based primer with a latex top coat. The primer that my paint dealer wants me to use is his “best” stuff, but it is a very fast drying latex type primer. When I tried to tell him my rationale, he counters that the paint has to let the wood breath. He allgeges that oil base will make the framing rot due to the moisture that cannot get out. I want the paint to stick. Who’s right? I have used a moisture meter on the wood everywhere and I don’t currently have a moisture problem but then I don’t haven’t painted yet either. I have tried his laytex primer and it bonds ok but not great. It doesn’t go deep at all. I can peal it off. For what it’s worth, this is old lap siding and I have cut it down to bare wood. No old paint.
This is bits from "Finishes for Exterior Wood", by Forest Products Society and is based on the work done at that the US Forest Product Lab.
First they recommend a Paintable, Water Repllent Protectant to be applied shortly after it has been prepped. Specially work it into the end grain at the joints.
Then for a primer they say;
"For woods with water-soluble extractives, such as redwood and western redcedar, the primer must seal in or tie up the extractives so that they will not bleed through the top coat. Usea good-quality oil-baased, alkyd-based, or stain-blocking acrylic latex-based primer .... The primer should also be nonporous and thus inhibtit the penetration of rain or dew inot the wood surfaces .... For species suchs as pine or others that are predominately sapwood .... a high-quality acrylic latex primer is preffered ..."
> I can peal it off.
There's your answer. You need a better paint system. You may have to test a few to find one that works well enough.
I used an oil primer on my 160 year old house, topped with the latex. 25 years ago I did a lot of painting, and oil primer certainly had a better reputation then. I used the oil primer this time after discussing it with the paint store owner - he has a chemistry background and an interest in his paint products - so at least he wasn't just shooting his mouth off. He really didn't see the oil as being all that much better than the latex. He said advances in latex paint and steps backwards in oil paint (formulation restrictions due to reducing VOC's etc) had basically put oil and latex on the same quality level. Now why oil for me? Adhesion. He really thought that oil primer was better at adhesion. In my case, i had a lot of old paint left on my clapboards after scraping, so the adhesion isse was not just of primer to bare wood but also adhesion of cracked thick old dry paint left on the surface.
It worked, at least for the past three years. I really haven't noticed and cracking or peeling.
My own observation about "bare wood" on the 160 year old clapboard was that I had a "soft" surface. It was like there is some thin layer on the surface of the wood that is soft. Very thin, such as 1/64 or even half that. I really doubt that I will get great long term adhesion in those spots, but my sense of it is that having used the oil primer on that bare wood was a much better idea than having used latex. That oil primer has a lot of time to work on saturating that top layer of wood.