Spirit

I must admit that I always use Limelite Easy-Bond but a lot of people find it a bit pricey. As you will be laying 65mm thick concrete, is is unlikely to move anyway on a keyed surface so a high quality bonding agent is unlikely to be of great benefit.

All of the PVA failures that I have heard about have been because of misuse of the product, incorrect dilution, dusty surface etc. This can happen with any product. I would imagine that PVA fails more than other products is that it is used probably 10 times more than all of the others put together.