Tying in blockwork to existing exterior rendered wall

[Phil the skip]

Good morning. Some advice please, I’m building a small extension to the rear corner of a bungalow which has rendered exterior walls. I’m nearly up to DPC ( see pic below ).
I’ll be matching the walls up with dense concrete block then rendering. Do I have to remove the existing render in a vertical 300mm strip to join and tie-in the new blocks?
I have bought heavy duty screw-in wall ties to join new block work. Many thanks.

 

[^woody^]

Yes.