“Radon Fountains” must always be sealed.
If Radon Fountains are not sealed, more hot, humid air must be added to reach the desired radon reduction. RESULT? Much greater risk of mold.
RADON ABOVE 8: If the Radon level is above about 8 picoCuries per liter, radon is probably coming from both the concrete and from the soil through a concealed “Radon Fountain.”
We know that in South Florida, concrete emits enough radon to create a radon problem in many condos, but not usually above 8-9 picoCuries per liter
We also know that radon can enter into the breathing zone from the soil. When it does, it is entering through an unsealed or poorly sealed hole in the floor slab. End units, especially those above sewer and electric service lines experience the highest radon levels. Code required that points where freon lines passed through the slab must be sealed with expanding urethane foam. Expanding foam makes a nice appearing seal, but it almost never forms an airtight seal. It must be removed, the opening dammed with backer rod and sealant, preferably an elastomeric, pourable, self-leveling urethane caulk. CAUTION: Toxic outgassing will occur for several days. Supply plenty of dilution air during application and for that outgassing period.
RADON ABOVE 12: In cases where radon is above about 12, the air conditioner air handler is often “mining radon by suction”: through a nearby slab opening and adding it to the radon emitted from the concrete
RADON ENTRY: SLAB OPENINGS/RADON FOUNTAINS: These slab openings are usually hidden from view inside wall cavities. The worst and most frequent offenders are where the air conditioner freon lines pass under the slab and enter through a hole in the slab next to the air handler.
MUST ALWAYS BE SEALED: These entry points/Radon Fountains must always be sealed. Sealing is labor intensive and requires very good workmanship to restore appearance.
If a radon mitigator chooses not to seal “Radon Fountains,” he must add an excess of hot, humid outdoor air which has the potential to create NEW destructive mold problems. WHY? Air conditioners do not often have enough extra dehumidification capacity for the extra humidity load if “Radon Fountains” are not sealed.