Thanks muchly for all your advice guys. Happily I have been given the time and funds to break the old slab up to use as a base for the new one. Nice to hear from a group of people who obviously take pride in their work.
Hi all. Read your post with interest as I often lay concrete slabs where i need to stick new to old. Years ago I did some work at guide dogs for the blind. I had to lay grano screed onto concrete. It needed to be resistant to urine as well. I used RoniFix which did the job. I put the grano down about 15mm thick and walked on it the next day. Great stuff although a bugger to get off your hands! I suggest you use gloves.