Development of a methodology for the application of vinyl paint as a radon mitigation barrier for interior spaces

Radon gas is a radioactive gas produced by the decay of uranium and radium, which occur naturally in soil and rock. Radon gas can migrate into buildings from the ground and, to a lesser extent, from building materials such as bricks, granite and concrete. The accumulation of radon indoors can pose a significant health risk, as its inhalation can damage lung tissue, making it the second leading cause of lung cancer after smoking. In 2013, the European Union adopted Directive 2013/59/EURATOM, establishing an average reference level of 300 Bq/m³ in inhabited areas and the obligation to measure building radon concentrations. In Spain, Royal Decree 732/2019 adapts this directive and establishes specific requirements to protect people from radon exposure. The main mitigation measures include sealing cracks, natural or forced ventilation, sub-slab depressurisation and installing radon barriers. Although current measures are effective, research continues into new solutions to further reduce indoor radon levels. This work focuses on developing an evaluating a methodology for applying a commercially available regular indoor paint to ensure that it can be used as an anti-radon barrier in walls. The results show that a vinyl paint can be used to mitigate radon in indoor spaces reaching a radon concentration reduction percentage of 82.25 %, and a diffusion coefficient of 7.48·10⁻¹¹ m²/s. The increase in the number of coats is proportional to the effectiveness for radon reduction per unit thickness, with the best results achieved at thicknesses of 90 μm. These results open the possibility of using decorative surface coatings to mitigate the access of radon gas indoors in a simple, accessible and low-cost way that contributes to improving indoor air quality and reducing the impact of radon gas on people's health.