Emulsion bubbling and flaking

[joness]

In our kitchen there is a patch on the wall (about 10" x 8") where the emulsion has been bubbling and flaking off. The plaster underneath has also become powdery.

The wall is plastered on the top of plasterboard - completed about six years ago. Underneath the plasterboard is an old internal wall. The entire plastered wall is dry (apart from a couple of spots about 2 inches by 3 inches which look a bit darker so may be slighly damp - although they are not damp to the touch) so I don't think this is a damp problem.

I'm not sure what to do. So far I have sanded it down to a solid surface.
I've heard about PVA being used to help provide the right foundation for subsequent layers of emulsion. Also about thinning down the 1st coat emulsion. There is also a product I've used in the shower room - a white anti condensation paint - but I'm not sure whether this could be used under a coat of coloured emulsion.

Please could you advise me on what steps I should take.

 

[Burnerman]

The plaster deterioration is a sure sign of dampness behind the patch.....whats behind the wall? Shower, drain, maybe?
John

 

[joness]

There are no pipes, drains, showers etc behind the wall. The patches I mentioned are not really very damp and are in a couple of separate places. The kichen does get a fair amount of condensation when cooking. However the problem of the flaking emulsion and powdery plaster is only affecting a small area of the wall.