RadonSeal Standard &ndash; Deep Penetrating Concrete Sealer (2.5-gal) | Basement Waterproofing & Radon Mitigation Sealer | Seals Against Water Vapor, Water Seepage, Radon Gas Permanently! MONEY BACK GUARANTEE USER-FRIENDLY  Non-toxic, non-flammable, zero VOC's. EASY TO APPLY  Spray or roll-on application. PERMANENT  No reapplication needed. PENETRATES - Does not leave a coating. Works by absorbing and reacting inside concrete.