46erjoe wrote:
Just bought our home 4 months ago. It tested positive for radon (but
just barely). The seller agreed to install an active radon reducer
fan-type. It runs all the time, sucking air from under the basement
slab. After recent testing, the radon leven was very very low.

I see is that there are many large cracks in the floor. Around the
outside edge runs a gap at least a quarter inch. Then there are
several shrinkage cracks also very large.

If I were to seal every one of these cracks with urethane calk and
thus make the basement airtight, would the radon problem go away?

Or can radon leach through concrete block and floors? I sure would
like to shut off that noisy 24-7 fan and convert it to a basement
bathroom vent to the outside.

Concrete is pretty porous, which is why moisture seeps through it, so
radon does too. But, companies sell the same kind of waterproofing
sealing paint they use to waterproof the concrete for radon-proofing as
well, as I discovered from searching the web. Of course, you need to
plug the cracks too. But in the case of a barely positive test, that
might be enough to knock it down below the legal radon limit (4 ppm,
isn't it?).