Unfortunately you have only two options. Peel and scrap the paint off and re-sand the walls or multiple costs of undercoat paint to mask the black.
Any primer or does the primer have to be a certain color.
Peel and scrape paint off the walls and resand? Sorry, but I don't think that is at all necessary. Why would you put yourself through that when any good quality primer should cover up blue or black? That's what primer is for. I successfully painted over Christmas red walls with just one coat of Zinsser 123 primer and followed up with 2 coats of pale aqua paint. In a worse case, you might have to apply two coats of primer. However, when in doubt, it never hurts to stop in at a paint store like Sherwin Williams and ask their professionals for their advice .
Regarding the color of the primer, it depends on what your new color is going to be. If you are going to be repainting a light to medium color, you can typically use the primer right out of the can. Generally, it is recommended you use a tinted primer before painting a dark color. Before I painted my walls red, I showed the guy at the paint counter the red I had chosen and he tinted my primer a medium gray, which was the recommended color to insure the red came out looking deep, rich and true to color. There was no tint added to the primer when I decided to paint over the red and go pale aqua. Again, rely on the paint professional at the counter to guide you based on your color choices.
I primed over black walls that my step son had painted. Then painted them butter-white. No problem. Just a LOT of primer! xo
There are very good reason why you don't put up to 10 costs of paint on a wall. Sorry ladies but you can't buy experience. Sure paint over it. But if the house is to remain your home for many man years to come then leaving that many coats of paint on the wall does have some cons. However, the blue shouldn't be a problem.
@Leevers : My husband and I lived in our previous home 36 years and it was 20 years old when we bought it. I know it had been painted several times prior to us, we painted many times during our 36 years there, plus we have allowed our renters to paint it colors of their choosing since we moved 2 + years ago. As long as the paint is adhered well with no evidence of peeling, I do not understand the need to scrape, regardless of how many coats are on the wall. Since this site is all about sharing ideas and knowledge, if you are a painting professional and know something we can benefit from, please, by all means, take this opportunity to educate us regarding the cons of having too many coats of paint on the walls. I'm all ears.
I'm not saying you have to scrape, however, to rule it out is not smart. If the original coat if paint was never primed prior to the colour then in time it will peel as the paint does not bond correctly. If you spend hundreds on paint over the years, it doesn't matter how many coats you put on, the peeling may still occur in time from the original coat thus costing you a fortune in paint only to have to go back and start again. Ultimately it depends on the surface you're painting, however, plaster is terrible for this. I'm not saying scrape it all off but don't rule it out without first identifying how many coats exist on the wall and how it's been original done. You might get away not doing this and I'm sure many do, but the more you know, the more money you can possibly save.
I'd love to hear from a Professional painter regarding this. Since I too, have never scraped paint off of any walls, ever, to 'get them ready' to be 'painted'. Maybe I fall into the lucky or dumb category. Heck maybe both LOL!!
When I painted white over our pine wood paneling that had been stained a red color, I used Kilz Low VOC and it worked great. You can see how I used it on this rocking chair here: http://www.prodigalpieces.com/2013/07/how-to-reupholster-paint-rocking-chair_11.html. When I worked on a paint crew for a couple of years it was our go-to product for covering stains, etc. Hope this helps! :o)
I am not an experienced painter - just a homeowner - and I would hate to have to scrape the walls. I will do the primer and listen to Shari or Sia - thanks and will let you know what was the result.
@Joellen Finnie You'll have beautiful walls, you'll see ;) Primer is the key! xo