Problem with plastered wall

[Mackem]

Two years ago I had a conservatory built against the brick side wall of my house. The brick wall was then dry-lined and skim plastered, except for an area of about one sq foot, which was plastered & skimmed to a depth of about 3/4 of an inch. After two months I painted the wall with a diluted coat of emulsion and then a full coat of silk emulsion. After about a year, the emulsion began to bubble badly in the area of the sq foot of solid plaster, so I scraped and sanded the emulsion off this patch and then primed it with a 1/5 diluted pva and then a full coat of silk emulsion. Now, almost a year later the emulsion on the same area is badly bubbled again. There is definitely no dampness present. I've asked for advice at my local B&Q and local paint shops but without success. Is there a solution to this problem? Any advice appreciated. tia

[John Rumm]

Odd, that is what it sounds like....

Hack off the plaster and dryline that bit to match the rest?

[Weatherlawyer]

Efflorescence is caused by water in the plaster. Why was this patch not treated in the same manner when the rest of the thing was plasterboarded? And how much water is being voided through the brickwork on the other side of the wall?

It sounds like that patch abuts a room that is usually steaming. A boiler, laundry, airing cupboard or some such?

Maybe the rest of the walls are getting the same problem but the gap between the wall and the plasterboard is providing enough protection to stop it being seen. Any woodlice or silverfish present there?