We had a small water leak which has damaged the paint work near the ceiling. I've scraped the paint back to the plaster, removing the damaged paint. Do I need to reseal the plaster and is there something I can use to make up the layers so that I don't need to scrape the whole wall? If I do need to reseal the plaster, what's the best thing to use and I think I've heard of something called a levelling compound. Is this what I should use or can I just build up with layers of paint?