All Purpose Foam Coat #025

Having been in the stage prop business for more than 30 years and using other coatings we tried your Foam Coat and While the foam coat powder mixes well, and is easy enough to apply I have found that after it dries it does not sick very well to the Owens Corning FOAMULAR 250
2" in.Extruded Polystyrene (XPS) Rigid Foam board and where it is a bit thin turns to a dusty powder when dried for 48 hours...?