Thomas Lyon
It can be plastered over as long as the surface is sound and is not coming away anywhere. My preffered method is to scrape the high bits off the artex apply a bonding plaster coat and then skim it. I know then that the artex is covered properly. Too many times I have seen artex skimmed and you can still see the pattern once its painted. One thing to bear in mind beforehand is artex was largely used to hide unsightly humps and bumps. Once the ceiling is skimmed these will show up like a sore thumb. If this is the case then another option is to over board the ceiling or remove the existing ceiling and start from scratch.
