Smooth-On URE-FIL® fillers disperse easily in Smooth-On materials. They can be added to materials in different proportions to achieve a variety of working properties and effects. Some fillers are designed for cost-savings, others are designed for specific casting effects or improved physical properties. Other URE-FIL® fillers are designed specifically for thickening materials for brush-on or trowelable application.
URE-FIL® 7 mixes well with urethane resins and castable epoxies and will improve dimensional stability (reduce the shrinkage rate of some resins, for example). It is also often added to materials to make them flame-resistant. URE-FIL® 7 can be mixed with Smooth-Cast® 325 and SO-Strong® color tints to create marble effects. The maximum amount that you can add to a resin before compromising the physical properties of the cured plastic would be 1A:1B to 2 parts filler. A mix ratio of 1A:1B to 3 parts filler will make the plastic trowelable, but the cured plastic will also be brittle.