Caulking basement wall to slab seam

Posted by PVR on June 11, 2007, 10:54 am

Radon is the heaviest of gases. Therefore it stays in the basement until
stirred up (by a forced air HVAC system). When the fan goes off the radon
will quickly drop down again.
10.8 PiC/L is very high. In these parts (Ohio) they recommend a max of 4.0
PiC/L with 2.0 recommended.
Sealing cracks and other openings will have very little curative effect.
Radon gas can easily pass trough solid concrete, particularly if there is a
Radon pressure from below (which there always is).
The best technique of Radon ameliorization is to use a pro outfit. They will
dig a hole in your basement floor. They then purge the local area beneath
the hole by lifting out some of the substrate. A 4" pipe is inserted and led
to the outside. An extraction fan is placed in the pipe. This fan is on
continuously.
Recently two neighbor's homes were provided with the technique described
above. Each was in the region of 10-12 PiC/L prior to installation. After
installation both properties were below 2.0. One company sealed all cracks
while the other didn't. No difference in the Radon levels. One neighbor's
house was a duplex. After installation he found that the neighbor's house
was also sharply improved so that his neighbors did not have to install the
pipe, etc. Cost of the installation is about $1000.00 +.
This is all very surprising because prior to about 1980 EPA had no
recommendations re radon amelioration. Perhaps prior to 1980 radon was not
poisonous (g). Radon itself is not all that dangerous because it is only
weakly radioactive. Unfortunately one of its decay products is polonium
which is strongly radioactive and being a metal it stays in the lungs.
Overall, your call.
Peter.
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Posted by barry on June 11, 2007, 10:36 am

> Hi,
> I detected some Radon exposure in my basement and am trying to seal it
> up to stop the Radon gas seeping in.
> I have a concrete basement, walls and slab floor. What I am trying to
> seal up is the gap between the slab-floor and the concrete walls. The
> gap's width is about 1/16th to 1/4 of a inch and varies depending on
> where you look in the basement.
> This is probablly a dump question but what is the best way to plug
> that gap? I tried using SikaFlex SL (Self Leveling) concrete caulk.
> But it just seems to pour into a bottomless void. I guess it must be
> the crush rock beneath the slab. I thought I would use this because I
> think if would give me the best air tight seal.
> Questions:
> 1) Am I using the wrong Caulk? I.E. Should I be using a non self
> leveling one. That way it would not drip into that bottomless pit. Any
> caulk recomendations
> 2) Foam backing rod. Could not find one thin enough, so ended up using
> window foam insulation. This does work, but it takes ages to slip into
> that crack and I have like 300 feet perimiter to do.
> 3) Should I be trying to fill the crack with some concrete first? If
> so is that a bad idea because you want some give in your basement to
> allow for thermal expansion etc.
> 4) How would a professional Radon company seal a basment? Can I
> replicate what they would do? i.e. am I doing this all wrong?
> Thank you for your kind help.
> Warmest regards, Mike.
Mike,
You're not going to be able to seal it out, not so long as the
pressure
drop across the boundary is zero or positive. Hint: you need to
evacuate
the radon from outside the boundary and exhaust it outside.
Meaning, typically a small duct under the slab kept at negative gauge
pressure by a blower, exhausting outside. Time to talk to experts.
HTH,

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