About to tile some bathrooms with heavy 10mm porc 600x300 tiles.

The walls have been plastered and painted.

Do i need to score the walls up? Bit concerned about the paints strength in holding up these tiles.

What sort of paint is it ? Ideally it should all come off, what doesn't come off do the tape test, but what is the substrate behind the plaster, is it block or plasterboard, you may be getting close to the weight limits.

if it's skimmed plaster I'd say that you'd already be exceeding safe load bearing limits with porc tiles

might be worth using backerboard or plasterboard to sheet the walls.

Its plasterboard, skimmed with a basic initial watered down white tosh.

Mmmmm, your going to be overweight limits for that substrate with skim, without the skim would be fine mate, see here for a list, any hope of you either knocking the skim off back to bare board or overboading ?

Originally Posted by Versatile69

Its plasterboard, skimmed with a basic initial watered down white tosh.

your porc tiles will be too heavy then, best to remove skimmed boards and replace with 12.5mm plasterboard or hardiebacker board