Effect of internal wall covers on radon emanation inside houses

Most types of paint for the internal walls of houses will reduce radon emanation from building materials. At the same time, the effect of paint will increase the concentration of radon inside the material itself and will increase the radon emanation from unpainted areas. One type of wall paper contains 6 and 0.3 ppm of uranium in its decorated and undecorated surfaces, respectively, the colouring being the main source of uranium. Other wallpapers appear to be free from uranium. Wallpaper, gypsum and plaster may increase the radon activity inside houses depending on their radium contents.