Ivy not clinging to wall

[Ffdan]

Hi all. I am trying to grow English ivy on a stone wall. The wall is slightly sandy but certainly not as much as sandstone or similar.

The ivy is growing well but absolutely refusing to cling to the wall! It isn't even growing any air roots to grip with... I cant understand whats going on. Internet search come up with nothing.

Any ideas?!?!.

 

[DirtMechanic]

The Exterior insulation finishing system may have antimicrobials mixed in it. Same goes for some well made paints.