How do you remove water stains from a ceiling?

[#1]

If you have a water stain on your ceiling, the first thing to do is ascertain whether there is an active leak in the structure of your roof. If you are not confident going into your roof space, I recommend you employ the services of a professional. Even if there is an active leak, you might not be able to find it.

The other day I was in the roof as we had noticed a water stain on the ceiling and droplets of water hanging from the plasterboard sheeting. When I got into the ceiling the top side of that ceiling board was bone dry - it was a complete mystery.

The reason for needing to track the source of the damage is that if we repair it, you might unwittingly conceal any further damage that could affect the roof's structure.

Once you've ensured no ongoing issue, you can thoroughly clean the ceiling sheet with Sugar Soap and then flush it off with fresh water. Wait for the area to dry before applying two coats of Dulux 1L PRECISION Stain & Mould Blocker following the application instructions.

Once they have dried, you'll be free to use your choice of ceiling paint to finish the area. The stain blocker stops the watermarks from transferring through your topcoat and re-appearing. 

I trust you'll find these step-by-step guides useful: How to paint a ceiling and How to remove mould stains from walls. - MitchellMc

Please note that if you have mould, it is already inside the plasterboard panel and there is nothing we can do to remove it from the inside. Using cleaning methods such as vinegar will only provide a surface clean and eventually, the mould will return. The sugar soap is to prepare the surface for painting, it will not remove the mould that is already there.

My colleague recommended using Dulux 1L PRECISION Stain & Mould Blocker to block the mould from coming out.  Once the primer is dry you can then use your choice of ceiling paint. - EricL