How to Seal for Radon With a French Drain

Radon, an odorless, colorless, radioactive gas, is a major cause of lung cancer.

Make an Inspection

Cracks in concrete and sump pump intrusions must be sealed.Cracks in concrete and sump pump intrusions must be sealed.
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.

Step 1

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

Step 2

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

Step 3

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

Step 4

Check the sump for gaps around the pump.

Seal Openings

Step 1

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

Step 2

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

Step 3

Fill the cracks, holes and gaps with dry sand.

Step 4

Soak the sand with Crack-Weld.

Step 5

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

Step 6

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

Step 7

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