How to Seal for Radon With a French Drain


Radon, an odorless, colorless, radioactive gas, is a major cause of lung cancer. Radon may seep into a building through cracks or openings in a French drain, an interior footing drain that utilizes a gap between the interior wall and floor. A cove base is a contoured molding intended to fit over and seal the joint between the wall and the floor. In order to mitigate the effect of the gas, a "suction field" is created whereby polluted gas is sucked out of the ground and out of the building in pipes that vent high, well away from any re-entry points into the structure.
The method, called a sub-slab depressurization system, requires the French drain and all other cracks, holes, intruding pipes, and sumps to be sealed. If the French drain or other through-slab intrusions are not sealed, the pressure is reversed and the fan sucks air back into the ground.

Make an Inspection

  • Check the concrete slab floor for cracks, holes, openings around pipes and other intrusions.

  • Inspect the French drain for a gap between the walls and the slab.

  • Determine whether the sump pump is a radon-sealed pump.

  • Check the sump for gaps around the pump.

Seal Openings

  • Clean and dry the areas to be sealed with a vacuum cleaner or oil-less compressed air.

  • Prime the areas to be sealed with Radon Crack-Weld or similar product.

  • Fill the cracks, holes and gaps with dry sand.

  • Soak the sand with Crack-Weld.

  • Replace non-radon sealed sump pump with a radon-sealed pump.

  • Install and seal a cove base over the sealed French drain.

  • Seal off existing cove bases and all pipe intrusions and wire chases with Pipe-Tite or similar sealant.

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