You can leave the paint on drywall provided there are not several coats and the tile epoxy will adhere with no problem.
Tile adhesive painted walls.
If the substrate is non porous porcelain tiles etc priming is highly recommended with webercol prime.
Ideal for small format ceramic mosaic porcelain and most gauged stone tile on walls or floors acrylpro may be used in areas with intermittent water exposure such as tub surrounds and shower walls.
Mix and apply the selected tile adhesive with a suitable notched trowel.
Sand with a medium grit sandpaper to create a uniform surface that s not too smooth.
For large tiles only a flexible tile adhesive like webercol flex should be used.
If the walls you want to tile are concrete walls with paint on them remove the paint before you install tile so the tile adhesive has something to grab onto and hold the tile in the correct place.
Acrylpro professional ceramic tile adhesive is a professional acrylpro professional ceramic tile adhesive is a professional formula adhesive with high bond strengths.
Thoroughly vacuum the area and give the wall a once over with a damp sponge or cleaning cloth.