Interactions between proppants and a zirconium crosslinked hydroxypropyl guar (HPG) frac fluid were examined using rheological test methods. The advantages of curable RCP over tempered RCP and sand have been well chronicled.1,2 However, one disadvantage of curable RCP has been its effect on frac fluid viscosity and breaker activity. By definition, curable RCP is chemically reactive, and the chemistry required to form bonds between grains can interfere with a fluid's crosslinking mechanism. Using a Nordman 5002 viscometer with real-time digital data acquisition, viscosity data were gathered to quantify the rheology of crosslinked fluid exposed to uncoated sand, tempered RCP, and curable RCP. Proppant effects on oxidative breakers were studied by direct proppant / breaker consumption titrations. In addition, leachate samples of curable and tempered RCP were analyzed using Fourier Transform – Infrared Spectroscopy (FT-IR); differences in leachate provided information on which chemical species were reactive in interactive fluid chemistry.