Bulging and cracking plaster

[1952dub]

Hi
Just moved into 15 year old bungalow with conservatory. Plaster beneath one window is bulging and cracking up. Tried removing all and replastering but has recurred. No sign of damp. Inside made up of 2 thin walls with polystyrere block between.
Any ideas??
Thanks

 

[trowelmonkey1]

hmm, pics would be good on this one.

symptoms sound like damp, how quickly did the problem reoccur once replastered? how did you re-plaster exactly? 2 coats? PVA?

have you stuck a damp meter on it?

 

[roughcaster]

pics would be good on this one.

They sure would.

Roughcaster.