You should clean the walls if the paint is not sound. Dirtex is good for that. As a painter, I usually try sanding first with a pole sander just because that is quicker than washing just to see what I'm up against. You just don't want to paint over something that isn't adhered because your new paint will just be trying to stick to that layer of paint that isn't adhered and that is a recipe for disaster.

If it is just wiping off, but not peeling off, I would treat it like new,porous dry wall. Use a good drywall primer, preferably 100% acrylic based rather than PVA. The goal is to wet through that "chalk" and bind to the solid substrate. That said, it wouldn't hurt to try a small area first to make sure it is not creating problems with lifting. After a couple hours, see if the surface has solidified and bonded.

It's not peeling. It's just like chalk wiping off. It looks to me like the current paint is just extremely thin coverage. So when I wipe, I have hardly anything on my white rag, but the previous yellow shows up.

So, definitely not primer+paint in one go, even if it's 100% acrylic? I'd use the same color.

I think paint and primer in one paints are fine when just re-coating walls that are in good condition and a mere color change is desired. Where extremely dry walls are encountered and adhesion problems are a possibility, I would stick to a traditional dedicated primer and a separate finish coat. A 100% acryluc drywall primer would be able to wet and bind that chalky paint and give good adhesion to the substrate.

Thanks so much, I will give it a go. Assuming that everything looks fine (literally) when I'm applying first primer and then paint, does that indicate the paint will stay on the wall? In other words, if it doesn't work, will the fail be already obvious while I'm painting? I might try first in the tiny hallway.

Not necessarily. Sometimes paint will stick initially and then release as time goes on.

I agree with Christopher Nelson. Primer is always best and Guardz is a pretty good one. If you can't find that in the stores you visit as not everywhere carries it Gripper from Dulux Paints is another good one. Having not seen it or done any adhesion tests or seen how easily the existing coating does fail priming is my advice.

If in doubt, make a couple square foot test spot before committing to the whole wall. I doubt you will have problems. I would give a little additional dry time for the primer, rather than the short hour or so that the primer can will state. It will suck up quite a bit of primer.

In terms of adhesion, Gripper is the best water based primer I have tested of all those I sell. The goal is top wet through and solidify that porous,chalky paint and bond to the solid paint below it. Gripper is also sold under the Glidden label at Home Depot. It is part of the growing PPG family of paints. World wide, PPG ( Pittsburgh Paint and Glass ) dwarfs Sherwin Williams.

OK, primer it is..... I didn't know that you can still buy paint that washes right off. This was painted by previous owner less than 4 years ago.

(I still remember the old days when all paint had first to be washed off....)

Yes. There is some very poor quality paint out there still. And with V.O.C. laws being lowered it has made paints less durable as with those compounds that is where some of your durability was coming from. If you buy the top line paints from Benjamin Moore or Dulux you should be fine to put over top. But as I said I really don't know how bad the adhesion is.

They used Olympic, but I think the problem was matte over a paint with much more sheen.

is it possible to but a clear flat finish ? i love the matte look of my grey walls and wanting to keep it that way withoutit having the issue of oil and food stains etc and then having to scrub will slowly remove the paint as i have two young children.