Painting - How to strip walls? or should I?

We recently purchased a home built in late 60's with a kitchen updated in the 70's. At some point, a plaster or plaster-like material (mastic??) was used on the upper third of the walls with faux brick on the lower two-thirds. My brother told me the walls would need to be primed (I purchased Kilz) before painting. In her zeal to "help" and surprise me, my mother painted the upper walls with the new Behr product on the market designed for kitchens and baths before the primer was applied. Immediately the paint has bubbled :wall: in some places and can be stripped right off the wall. I realize paint stripper can not be used, and do not relish the idea of sanding....I do not know if there is lead paint on the walls. At some point there was paint as I have seen other colors under window hardware.
Would I be able to sand those identified spots to smooth out the wall, and paint the Kilz over the top? Or would that create a bigger problem? Any suggestions would be warmly welcomed as I really want to get this kitchen project completed before family arrives for Christmas. Thanks! Nancy

Welcome to the forums

I would scrape what you can and then sand. The sanding wouldn't have to be perfect - just to rough up the surface and maybe remove anything missed with scraping. You can then use joint compound or spackling to dress up any rough edges. Then prime and paint.

Would I be able to sand those identified spots to smooth out the wall, and paint the Kilz over the top?
That should work
Like marksr says, scrape what you can, smooth it out with joint compound if you have to

thanks for the guidance! :) Nancy

It is not a good idea,but I think you probably could have applied just the paint and it should not have peeled if the walls were clean. You may have had to do an extra coat or 2[with any paint],but it shouldn't have peeled, at least the way you describe.

I think it probably had grease on it[like all kitchens],and needed to be cleaned. Never paint a kitchen without cleaning first. Joneq likes Soilax pro. Probably too late for the walls,but if you were planning to paint let's say the ceiling===Soilax Pro it. No rinsing and does not redeposit the grease. Probably the best all round cleaner imo. Great before painting.

Nothing should be put on the walls before it is cleaned. After you get done scraping and sanding clean it with the Soilax. It doesn't take long and like I said there is no rinsing. wipe it on wait a sec and wipe it off.

Not saying your house is greasy,but doing anything like what you are talking about requires a clean surface,even applying joint compound imo.

Soilax Pro is available in your local paint store-Not the Depot or Lowes.

BTW what made your brother think it had to be primed. I am not saying it didn't just curious

I know the walls were not prepped properly by my mother, which I am sure is a contributing factor.....she basically slapped the paint on the walls. Not knowing what type of "plaster" product was used, my brother felt that priming was in order.
Thanks for the recommendation for the cleaner. I was only going to use water to wipe the walls down after the sanding. I appreciate the guidance! :) Nancy