Caulking basement wall to slab seam

[hobbes]

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.

[ransley]

I would fill it with mortar mix.

[hallerb]

mortar mix then caulking..... mrtar mix prevents caulking from falling in.

caulk the sills on all walls even interior ones. and any floor openings like bolts or boards bolted to floor.

you preping the home for sale? this usually comes up then.

radon mitigation companies seal everything then install a exhaust system ' how high was your number

[hobbes]

I am not selling. But the state (NY) had this DIY test offer for 7$US for any NY resident. So I thought I would check and see. My living space was 1.2 PiC/l and the basement was 10.8 PiC/l.

Best, Mike.

[hallerb]

yeah thats high. do you have any basement ventilation? a friend had numbers like that, added a computer muffin fan to a extra dryer exhaust vent he wasnt using.

end of problem he said fan used about a buck a year of electric, he left a small entrance vent so air could flow easily.

i would definetely get it fixed somehow.

[barry]

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, J

[PVR]

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.