Andy, this is what I would do, and you can take it or leave this advice. In situations like this (and funnily enough I have a similar situation going on right now). Tomorrow morning I am issuing a 'disclaimer' because I am now seriously under pressure to bring a contract in on programme. It will basically state we will undertake the works as instructed but we accept no responsibility, in any shape or form for any failures, as a direct result of the substrate not being ready to recieve the material.
The client then signs and dates it, and you carry on.
Basically you throw the problem right back at them.
Good luck
Lynn