I'll describe the symptoms and perhaps you can tell me how to proceed.

I have a lot of repainting to do of an old house and have noticed a few things.

The first situation is when I removed wallpaper from the bathroom and saw there was a thin layer of white paint which was applied over a previous layer of yellow paint. The yellow paint seems to be very well adhered to the original wall surface, but the white layer flakes off the yellow paint leaving bare patches. You can peel some areas of the white paint layer from the yellow paint surface with your fingernail.

The second situation is that the original paint on the doors and trim in the same bathroom is a mauvey gray, and when I painted directly over it with latex finish paint, I could similarly flake the new paint from the original paint with my fingernail.

I can't have the new paint finishes in the house subject to being easily rubbed off.

My thought is the two cases may be related, in that the yellow and gray paints may be possibly alkyd? In the case of the white layer over the yellow, the white layer may have been latex, so never had a chance to adhere properly to the yellow (alkyd?). The same explanation may apply in the case of my trying to paint the new latex finish paint over the existing (alkyd?) gray paint.

I don't know if that makes sense, or if there are other factors which may be in play.

How would I handle the wall situation. How do I tighten up the substrate (the flaking badly adhered white paint surface, so I could apply a solid paint finish (hopefully in latex). Do I have to remove the white layer first, or can I hopefully paint over it to "tighten it up" with a latex primer or other product, which will allow the new finish paint to have a solid base?

The same question applies to the trim situation.

This is just one room at the moment, and I'm sure the same syndromes will show up throughout the whole house, so I have to find out how to resolve this.

Thanks for your help with this.

Ted