<p>Magnesium aminoclay (MgAC) has been applied for different purposes, from biological to environmental applications. Herein, we used MgAC as an additive in the water-soluble epoxy coating solution for antiradon applications. Water-soluble epoxy can fully exfoliate MgAC and has low volatile organic compounds. Results indicate that the appearance of MgAC at low concentrations increases the antiradon efficiencies of epoxy coating solution in both laboratory-scale and real-field investigations. Different techniques, including X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and thermogravimetric analysis, are used to investigate neat epoxy and MgAC/epoxy composites. MgAC is fully exfoliated, and its existence in epoxy does not significantly alter the structure of the epoxy coating agent. However, the amine groups of MgAC interact with an epoxide group. This reaction could lead to the absence of structural defects observed in the neat epoxy samples, thus improving its antiradon efficiencies.</p>