How do I stick plaster mould onto a rendered pillar?

[SLIPPY]

Im looking for some advice guys.
I am doing a job tomorrow that involves some rendering, the customer has also asked me to stick on 4 plaster moulds onto a set of gate pillars that have been rendered in the last few weeks. I have never done this before and was wondering what is the best way to do this. Do I use gripfill or something similar. Thanks

 

[SPREADS]

Chemiacl mortar who be a good job ,you wont have to wait to long for it to set.

 

[theblones]

floor tile adhesive

 

[SLIPPY]

Im gonna use powergrab, thanks for replys.

 

[Render Systems]

make sure that you score the new render quite deep also i would use a few mechanical fixings as well (screws) as if the render is the slightest bit damp the mouldings WILL fall off