Can you vandex over blackjack?

[Dan1million]

Evening all, I've removed a load of render from the inside of the front wall of my house and it's got a layer of blackjack on it. I want to coat in vandex but do I need to remove the black jack first or can you apply vandex over the black jack?

 

[Stewie03]

Yes

 

[Dan1million]

yes it needs removing or yes it can be applied over it. I've two builders who say the opposite.

 

[Stewie03]

yes it needs removing or yes it can be applied over it. I've two builders who say the opposite.

you got any gear just do a test patch on it,from what I remember when black jack was applied they threw sand at it whilst still tacky any of the builders black and called jack