Help and advice

I would be very grateful for and advice on the following problem
I had a single storey extention built last year and the initial scratch coat was done in sections in December last year and the second coat was done in late jan/ early Feb. Large sections of the render are now blown, and after speaking to the builder he is saying it is because I have not painted it? I have chipped a bit off and the outside coat is very hard but the inside scratch coat is like powder/sand and poured out the...

Help and advice