hi Nestor, I have read a few great threads of yours which have been very helpful. My situation is that we have removed wallpaper and the glue from the plaster wall in the bedroom of our 1924 house. There appear to be at least three layers of paint--probably more, and i'm guessing some were oil. The walls were lightly sanded after i took out wallpaper and glue. I had a plasterer come by and repair the major cracks for which he used plaster weld; he then used a mix of standard joint compound and easy-sand setting joint compound, mesh, etc. there were many small scraped areas of the wall, where underlayers of paint were visible, most of which also had plaster weld applied before spackling. (The glue was so stuck on the wall in sheer desperation i sometimes had to scrape it off.) I gather I should spot-prime these areas before priming the entire wall. The dilemma is whether to use an oil-based primer to stick better on these old walls or some other strong latest primer. all the hardware guys say oil. I don't mind that, but the people at buildingscience.com maintain that in my NY summer hot/humid climate, oil paint is a vapor barrier, and during summer the oil paint would act as a vapor barrier which would prevent moisture from drying to the inside. So i'd prefer a latex primer if possible. I'm also curious to know if it's a big deal if the plasterer did not put plaster weld on all the little scraped areas before spackling. These are inches small areas. Thanks.