S.W.C. we're kinda on the same track thinking that any break in the coating will cause a paint failure and peeling. I guess the way I'm thinking is that different substances may expand at different rates in the same temperature and the less dense or "larger" molecules of latex will expand a greater distance and its just because of the oil being able to penetrate and bond to the latex as it expands that will cause it to crack and then the "break" in the film happens and then the peeling starts..Its just a way of thinking about it ...I could be wrong.QUOTE=S.W.C]When I say more dense, I mean that the molecules in oil are closer together than in latex, like silicone or teflon, the molecules are so close together that compounds with a less dense structure can't penetrate them (it's like putting gravel in an hour glass), but the compounds with the more dense structure penetrate very well, because their molecules are small enough to get in between other less dense molecules, such as those of latex based paints.
I agree that latex forms a continuous film, especially on slick surfaces, such as oil.
The problem there is, it doesn't penetrate at all, so it's basically just rapped around the oil, and any break in it will cause it to start peeling like a bad sunburn.
I've done repaints where the previous painter applied latex, satin or semi-gloss, over oil(ten years before I got there), it was still on, and I couldn't tell it was over oil, untill I started to scuff it up, then it started flaking off with just light sanding.
Of course their were no children or pets in the house, so it didn't get any wear and tear.
Oil over acrylic based primer, not acrylic paint, works for porous surfaces, for smooth surfaces you need a primer with a denser structure so it will penetrate the surface, but yet allow the oil to penetrate it, that's the way I understand it.
It's a matter of matching the primer to the surface, and then matching the paint to the primer. :Thumbs:[/QUOTE]