Adhesive bonding old and new - Tile Advice

[Ryanbon]

Hi all, I have a fully cured sand cement screed that howeever needed proper levelling and prep work before installimg my 120x60 Porcelaine gres tiles. My contractor proceeded in using adhesive as he advised that he can use tile adhesive to level it up rather than self levelling. Unfortunately due to unforseen shipping circumstances my tile shipment that was due on same day has been messed up and now I ended with dried up adhesive and will have to wait a couple of weeks before new shipment comes in. Tile layer is saying that it will be no issue to bond the new adhesive with old but I am really concerned as never in my experience have encounter this kind of technique so would appreciate any professional advise. I am not sure if best way forward would be to remove old adhesive altogether and re-start process again or there is nothing to worry about. Thank you i. Advance for your time!

 

[GAZ5518]

Pictures would always be helpful…
Adhesive will adhere to old adhesive providing the old adhesive is sound.