"blister" between plaster and gunite in my older p

[MissyPoolGal]

Can anyone tell me the proper name for a blister that has appeared (and now broken through the plaster layer) between the gunite and the plaster layer in my older swimming pool. My not very helpful pool professional called it "skaling" but I can't find anything on it. I have seen this condition referred to as a "pop-up" one place on line.

I want to know what this is really called so I can learn what to do about it. Any help is appreciated!

[Guest]

bond failure, pop-off, delamination, maybe spalding if its through the thickness of the material