The structural stability of soil is a physical characteristic that affects soil degradation processes. Calcium-based amendments, such as calcium carbonate, calcium sulfate, and calcium oxide/hydroxide, have been shown to improve the stability of soil aggregates. This study seeks to determine which calcium-based soil amendments, and at what concentration, are the most efficient in improving aggregate stability of sandy topsoils derived from granitic and metamorphic parent materials, and to analyze the mechanisms involved. In the pot experiment, soils amended with CaCO3, CaCl2, and CaSO4 did not present significant differences in aggregate stability compared to the control or among each other. In contrast, Ca(OH)(2) soil amendment brought the greatest stability to the soil aggregates. A dose of 1% Ca(OH)(2) significantly increased the stability of soil aggregates. This effect is due to the reaction of Ca(OH)(2) with atmospheric CO2 which leads to the formation of CaCO3, a delayed reaction not showed by the other soil amendments tested. Likewise, the greater solubility of Ca(OH)(2) compared to CaCO3 exerts a greater aggregation effect on soil. Thus, the mechanism of action of Ca(OH)(2) is related to cementation, rather than flocculation. Future studies should be carried out to demonstrate the effectiveness of Ca(OH)(2) under field conditions.