Boss Plaster ? Why does it happen ?

[self builder 123]

Hi

My builder told me that the plaster on the outside of my house is "boss" ?

Why might this have happened ?

The plaster is made up of 4 parts sand and 1 part cement.

When you tap it sounds hollow in places and when you hit it, it falls off the concrete blocks behind cleanly as if it was never there ?

Could the frost have got to it when it was curing ?

 

[ColJack]

from what I understand..

if you apply plaster or render to an un-bonded wall ( IE, not sealed with PVA mix ) it sucks all the moisture out of the plaster in contact with it drying it out before it cures properly so it just turns back to powder..
this means it only sticks to the wall in a few places and tends to just fall off..