The Hedvall effect was used to investigate the reactivity of calcium silicate hydrates (C–S–H) with variable C/S ratios. The solid state reaction between silver nitrate and various C–S–H preparations occurring during the crystalline transition of silver nitrate was evaluated. Thermal methods as well as microscopic and X-ray diffraction analyses were employed to study the nature of the reaction products and estimate the chemical reactivity of the C–S–H systems. The overall reactivity included cationic and anionic species; namely both calcium and silica entered into the reaction. Silver silicate was identified as one of the reaction products.