Dave,Len & Colin,
Thanks for your posts.
Info useful particularly about hot pre-spray and dwell time.
Len,
I have had some good training but am just short in cleaning experience. In my defence the food grease layer was not just a layer on top of a heavy wilton but had gone through the pile to a depth of about 3/8ths of an inch in a small area of 24'' x 24''.
I know you are are right on the dwell time and as I suggested I was going for overkill.
regards
Eddie