Help with rendering advice

[Lillyprint]

Hi. Any advice would be appreciated.
We had our entry wall rendered a few year ago, it was then painted with bitumen.
It seemed to have some sort of reaction. The bitumen is flaking off and there are big patches of white chalky places
We are looking to have the existing rendering taken off and getting it done again. However I am getting conflicting information. Should the wall be sealed before being rendered again.i gave read some say yes it should but others say no it should not.
Help please, I am going round in circles.

 

[Deleted member 265726]

Post some photos of the wall and the 'chalky places' so others can see.

 

[Lillyprint]

Thank you, will put a couple on tomorrow.