The reaction-to-fire properties of wood can be improved by the application of fire-retardants. However, a wide variety of fire retardants are of ecological and health-issue concerns. The objective of this study was to investigate and compare the effects of various harmless and eco-friendly salts and after carrying out a 2-step mineralization process to obtain a calcium oxalate mineralized beech (Fagus sylvatica). Two mineralization formulations to obtain CaC2O4 were applied. First Formulation was a combination of the water- soluble salts K2C2O4 and CaCl2, where the second formulation was a combination of K2C2O4 and Ca(CH3COO)2. The two particular salts were impregnated into the wood, successively. These salts are intended to react in-situ to the heavily water-soluble mineral CaC2O4. To determine the impact of the various precursors, the reaction by products, which are appear during the mineralization process, as well as various retentions were focus of this study. The thermal behavior of the various treatments was determined by means of TGA measurements. The reaction to fire was carried out with a mass loss calorimeter.  Special emphasis is set on the impact of the precursors and by products on the thermal behavior and the reaction to fire, as well as the performance of CaC2O4 after the by-products were leached out. An influence on the thermal degradation of beech wood after treatment with the salts and after the 2-step mineralization process could be demonstrated. Furthermore, the impact of various precursors and by-products on the reaction to fire was determined. Thereby, chlorine containing treatments show to have the biggest impact in improvement of the fire retardancy of wood. However, after leaching of the by-products, specimens which only contained CaC2O4 indicate satisfying improvement on the reaction to fire of the beech.