Epoxy resins need modifications by rubbery additives, fillers, etc. for enhancement of their usage in various applications. This study aims to determine the mechanical properties of silicone (i.e., amine-containing poly dimethyl siloxane)-modified resins in combinations with fly ash. The mechanical properties, especially tensile/flexural strength and moduli, were determined. Amine-containing silicone (ACS) was found to weaken the epoxy resin. However, ACS-modified epoxy resin was found to tolerate the addition of a small amount of fly ash filler as it had better tensile and flexural strengths compared with the unfilled, modified resin. In contrast to this, the unmodified resin was found to have its tensile and flexural strengths deteriorated by the filler. The reason for this behaviour was speculated to be due to the ACS acting as an additional coupling agent between the resin and the filler. These properties were sought to be correlated with free volume parameters measured from Positron Annihilation Lifetime Spectroscopy. Free volume measurements appear to indicate enhanced epoxy-fly ash interactions by ACS. Scanning Electron Microscopy indicates better filler distribution in the ACS-modified resin compared with the unmodified resin.