Radon: odourless and unnoticeable – but manageable

The author of this blog is Kimmo Huttunen, Head of Product Group Management in Kiilto Construction.

Nowadays, we know that the features of the Nordic terrain, such as eskers, were created thousands of years ago by the ice age. The ice age cannot, however, be blamed for the source of radon, i.e. our geology, the granite rock that makes up most of our soil.

Since many people have opted to build their house on a rock or hill and a basement foundation is a good solution for building on sloped surfaces, they have often also been exposed to the invisible, odourless health risk called radon. Even though plots on high ridges with beautiful views are not often available nowadays, building a house on clay may not be the safest solution either – at least if you choose the most common method of building the foundation into contact with the ground.

Even if the soil on the plot is compact, radon may be carried along to the plot in the form of aggregate used for the building’s subfloors. The radon content of the soil aggregate found in the Nordic countries is among the highest in the world. For the same reason, the national recommendations for the maximum radon concentration in indoor air are less stringent than the WHO recommendation of 100 Bq/m3.

Traditionally, efforts have been made to prevent radon from entering the interior of the building by blocking any air leaks from the soil under the base floor to the indoor air. For this reason, ensuring the airtightness of the joint between the floor slab and the walls, as well as any penetrations, has been considered especially important. New studies regarding the diffusion of radon through concrete have shown that the material’s diffusion resistance is not constant but decreases as the slab dries.

This means that radon may even penetrate intact concrete, and the drier the concrete gets, the more radon passes through. Modern methods of construction usually include installing more insulation under the base slab than just a few decades ago, and the floor is also often used as a heating element. Due to these factors, the slab becomes drier than with previously popular methods. Considering the moisture aspects, this is a welcome development, but it also comes with a side effect that should not be ignored.

Radon can be prevented from entering the interior of the building via air leaks by ensuring that the base-floor structure, along with any possible cracks, is airtight. With the correct sealing product, the concentration of the gas coming from under the slab can be reduced below the recommended limit even in areas where the concentrations in the soil are high.

The Kiilto Airblock products can be used for radon protection in walls (basements) and floors, as well as for sealing any structural joints or penetrations. The product family includes both a low-viscosity product that can be either sprayed or applied using a roller, and a thicker, thixotropic product reinforced with fibres that can be applied with a brush. The solvent-free, single-component products are extremely easy to use, and the required two layers can be applied on top of another while the product is still wet. These features make Kiilto Airblock a fast, cost-effective and reliable solution for comprehensive radon management.

Kimmo Huttunen

Head of Product Management, Kiilto Construction