Painting bathroom walls

We need to get a bathroom wall (plasterboard) re-painted, behind which there was a leak a year ago or so. The wall is now discoloured.

We think that all is dry now and would want to have it re-painted with a mould-resistant white bathroom paint. Is there any need to treat the wall somehow before painting it?

Another wall in our flat preciously had yellow patches coming through, and then the decorator sprayed on something to block anything come through, before re-painting it.

I was wondering whether this may be recommendable to do with the bathroom walls now? And if so what that blocking spray (or any other method to do the same) is called?

Many thanks for any help.

----

One other question please: Is it quite usual for a relatively small scale job to just pay the total after the work is completed to our satisfaction?

It would be a good idea to paint a stain block over the water stained area. You may get away with using some oil based undercoat if you have some lying around as this will do the job and can be cheaper.

Once dry you will be able to over paint with your desired emulsion. Johnstones do a decent quality anti mould acrylic.