universal bonding conpound (for bonding plasterboard to wall

Yesterday I put up 5 boards in the new kitchen and had to join onto the old stuff. It was about a 10mm gap but lower than the new stuff by 10mm also. So I used the bonding on top of the old plaster to bring it level.
But my plaster is saying multi finish will not stick to the bonding when he skims it? Is this correct? Looks a good surface to me to finish on? Anyone any experience of this. Thanks

Get another plasterer !!!

As long as the Bonding Coat you put on is well keyed/PVA'd to the old surface, there should be NO problem. A good plasterer would know that. As all a plasterer would have to do is to PVA over the Bonding you put on, just to seal it/kill the suction, let it dry, then PVA it again and skim onto it right away while the pva is still wet/tacky. I think your "plasterer" seems "very unsure" about how to do the job. As Roy says, "get another plasterer".

That's what I thought? Isn't it meant to be plastered on😊