Radon is diffusing up from underlying soil/rocks through my basement's concrete slab. What is an effective paint/spray application to stop this?

I see RadonSeal (sodium silicate) ads claiming to help here, but I also see a lot of doubts in online reviews. Polyurethane caulk also seems to be an option, but it is not easy or normal to apply caulk to a flat uncracked surface.

I know the normal defense here is a radon mitigation fan to suck out gases below the slab, but I'd like to test a more energy-efficient solution first.

  • I would also doubt a paint/seal being to helpful if 4 inches of good concrete does not stop it. Opening a couple of basement windows/vents should help. Need testing to tell.
    – crip659
    Commented Aug 18, 2023 at 19:20
  • Do you have a sump pit? Have you provided that with a sealed cover and a vent, if so?
    – Ecnerwal
    Commented Aug 18, 2023 at 20:13
  • 1
    Present at what level? Dosage matters. My own place tests positive but at a concentration where I'd have to be living in the basement for it to make a statistically significant difference.
    – keshlam
    Commented Aug 18, 2023 at 20:14

1 Answer 1


The soil suction solution is normal precisely because it works. If magic paint worked, magic paint would be normal. I did a good deal of research when I found that the radon fairy had visited my building. I don't even have a basement. I'm very wary of 24/7/365 electrical loads. Based on research, I have a fan.

If you look around for a good one, you can get a radon fan that runs on 17-18 watts (12.5 kWh/month, pretty much.) That will be effective (no telling if it will be effective enough for your particular case until you try it.) [You can also get much less efficient ones, so I recommend shopping carefully with that in mind.]

Merely sealing, by any means, is not generally considered to be effective without a fan, or at least a passive duct. It can make a fan work more effectively, but by itself, if you have a problem that rates remediation, it probably will not be effective. Maybe if you have 5 pCi/l (185 Bq/m3) and are trying to get below 4 (152.) If trying to get to 2.7 (100) or less you'll almost certainly need a fan. If starting much higher you'll pretty much definitely need a fan.

Silicate surface sealers (I'd go looking for one not purporting to be a radon product, as they are pretty much the same and I bet that one costs more) are intended for the "flat expanse" case - caulking is for cracks and gaps at the edges or penetrations. Neither product does the other job well, so if attempting to seal the floor you'll use both product types.

  • As for my question, which is precisely the "flat expanse" case, I think your answer is that silicate is the best. I just wish there was some published data to help me estimate the amount of cut I can expect in the 1D "flat expanse" case.
    – bobuhito
    Commented Aug 18, 2023 at 20:21
  • If you're going to follow this through, please post an answer when done reporting your radon numbers before and after the attempt. Since your slab surely has edges, and most have penetrations, some caulking is to be expected as well as any surface sealing.
    – Ecnerwal
    Commented Aug 18, 2023 at 21:05

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