1. Check with some local precasters regarding economical details. They manufacture and install these structures all the time and have a wealth of knowledge.
2. There is a lot of debate regarding bonded vs. unbonded toppings on precast, should the topping count as part of the structural element. Personally, I say no, treat the topping as the wearing surface without any structural capacity.
3. While an epoxy bonding agent provides a strong bond, if your project is in a cold climate you should carefully research the epoxy you use. The coefficient of expansion for concrete and epoxy are very different and there have been cases where the topping has been damaged in freezing temperatures. Most applications in my area use a cement/sand grout as a bonding agent, sometimes with a laytex bonding agent added.
4. Lastly, if you are sure you want to use the epoxy, contact a few manufacturers like Sika, Chemrex or Master Builders for information.
