Wife just wants ceramic tiles in the tub and shower area. Wants to remove the
4" existing tiles and in the rest of the bathroom tiles have been there since 1951. And just wants to paint it. What will I find after removing the tiles, will I have to replace construction board or whatever they used in 1951. So I have a smooth surface for the paint?

If the cap tile is about 1'' farther out then wall above, u have a mud job.Uwill have to remove the mud and bakcer board and install S/R.

If tile is only about 3/8'', u will have to remove sub strait and install S/R. U will not be able to clean adhesive off whatever tile is mounted on.

Chuck

If it is backer board, if you install new backer board can you just paint it.
Without tiling?

If it is concrete board, the answer is no.

If u use S/R to redo the section can, it be painted.

Chuck

I don't think cement board was around that long ago.
You probably have Sheetrock or some sort of plaster lath walls with tile. I think best to gut the bath and start over painting tile that is that old won't get you far.