Covering damp patch

[divvy]

I've discovered a hidden damp patch downstairs it was a small drip over months, all has dried out so all I have to do is make good. I've been told if I paint straight over I will still see the patch, can I apply a special undercoat / bonding coat to hide the marks? If so can I buy it in B&Q or a specialist shop? They are solid brick internal walls if that helps and the plaster is all good.

Thanks in advance

 

[dextrous]

Stain stop paint - readily available anywhere, or even oil based undercoat should do the trick.

 

[Zampa]

Oil based undercoat.

 

[roughcaster]

Oil based undercoat

It works every time too Zamp'.

Roughcaster.