This is a great resin for achieving more of a "stone" feel to your finished casting.

Poly 15-3 is a 1:1 mix, filled polyurethane liquid casting plastic that has a 18 minute working time and a ~20 hour demold time. The filler in Poly 15-3 gives it a dense stone-like feel making it ideal for back-filling cold cast bronze parts. The filler also makes 15-3 a very economical, low-cost resin..

Photo shows a rough casting in the actual cured color.

Technical Data: Poly 15-3X - Datasheet
Poly 15-3X Part A - MSDS      Poly 15-3X Part B - MSDS