Another thing we have used in reducing(not stopping) shrinkage in epoxy. PUR, and polyester castings is temperature control of casting materials and the reinforcing. The term "exotherming" is generally applied to this heat creation caused by chemical reaction. This is necessary to attain structural strength and integrity of your finished component. If you need further advice regarding reduction of shrinkage, I could suggest you contact the technical departments of either
Sika Group | Sika AG ,
Dow Chemical Corporate Website - The Dow Chemical Company , or any other top line epoxy manufacturer. The are generally very helpful. I have been involved with mold making in epoxy, polurethane and polyester and other materials for over 25 years and have always referred any queries to the relevant chemists in involed and have saved a lot of money and time by not trying to hack it on my own.
When I have spare cash and time I love experimenting!