Is this indication of lime reaction

[Michael Rosen]

A few weeks ago I asked for advice on this bubbling paint and you kindly suggested it was a lime reaction to vinyl Matt emulsion

So I stripped back the paint yesterday to apply a coat of Guards and this is what lies behind the blistered paint. There seems to be a darker spot within the plaster. Does this confirm the view above that this is a lime reaction with the emulsion in this particular patch?

Attachment​

 

[Wayners]

Looks like gypsum multi finish plaster?

 

[Michael Rosen]

I'm sorry I don't know. This wall would have been plastered long before we moved in 12 years ago.