Designing Kitchens and Bathrooms - removing plastic wall tiles in bathroom

We have an old home (1925) with plaster walls and our main floor bathroom has plastic wall tiles over plaster walls. We want to remove the plastic tiles and replace them with ceramic tiles as we have marbLe flooring and the plastic tiles just look TERRIBLE! Can anyone advise best process for this. Or, is there a way to put ceramic tiles OVER the plastic tiles? THANKS!

Plastic wall tiles. Huh, that's a new one for me. Any how, is the area you're talking about a wet area such as a shower or mainly walls that don't customarily see a lot of water? Have you tried removing any of the tiles to see how it effects the plaster wall? I'd be concerned the removal process may render the plaster unusable requiring the walls to be redone. Not being familiar with plastic tiles, I can't speak from experience, but my guess is, no, you shouldn't try to install ceramic over them. You don't know how well adhered the existing material is so it may not support the weight and I wouldn't think you'd get much of a bond to them.

Thanks, Smokey49, for your reponse. There is no problem with moisture as this is a "powder room" and, although there is a sink and a toilet, moisture shouldn't be a problem. I think these wall tiles were popular back in the 50's and 60's. But I think your advise about NOT tiling over them is probably correct. There may be no other way than to try to remove one in a inconspicuous location and see how it effects the plaster. Anyone know how big a project it is to put ceramic tile on a wall with a plaster base? THANKS AGAIN!