basement prep for radon

Old 02-03-04, 06:33 AM
Visiting Guest
Posts: n/a
Question basement prep for radon

We are beginning the very slow process of finishing our basement. We already know we have a radon issue and plan on installing a pump. From what I have read, it makes sense to seal all cracks in the floor and gaps between the floor (poured concrete) and perimeter walls (block) so that the pump isn't drawing inside air. We don't have too many cracks/gaps and those we have are small (<1/4 inch). The basement is dry so I am not sealing for water.

Since it makes sense to do all this now, before framing, can you help me understand what kind of caulk/sealant might be best?

Thanks. This website has solved many problems for us.
Old 02-03-04, 07:06 AM
Join Date: Dec 2003
Location: USA
Posts: 929
Upvotes: 0
Received 0 Upvotes on 0 Posts
So where exactly will the pump be drawing from? It isn't clear from your post what you're trying to do (other than seal the floor).

You say you know there's a problem. How? Has your home been tested for radon? Assuming yes, you need to consider the level detected vs. the amount of time per day you intend to spend in the basement to see if remediation is worthwhile. Having worked in the nuclear industry for more than 30 years, it's my opinion that the whole radon issue is overblown and not nearly the hazard it's purported to be. Big money maker for contractors though.
Old 02-03-04, 07:30 AM
Join Date: Aug 2000
Location: USA
Posts: 15,047
Upvotes: 0
Received 2 Upvotes on 2 Posts

State guidelines for radon control tend to vary. It is best that you contact your state radon office for recommendations.

National Radon Hotline:

In addition to radon resistant construction techniques and radon reduction systems, sealing cracks and other openings in the foundation tends to be a basic part of residential radon reduction in order to reduce the flow of radon into the home and the loss of conditioned air. Sealing should not be the only control method used, as sealing tends not to lower radon levels significantly or consistently. It is nearly impossible, however, to identify where radon enters and to permanently seal all the entries. As homes settle, new entries tend to be found and sealed ones may reopen. (

There are special radon sealants available for basement concrete, such as Radon Seal. Because radon atoms are much smaller than water molecules they flow easily through the pores in concrete. The sealant reportedly seals microscopic capillaries deep inside concrete and makes radon levels below 4 or 2 pCi/L readily achievable. Any openings and cracks should be sealed off or caulked to stop radon, as well as moisture and soil gas, in and around crawlspaces, sump pits and floor drains, wall/floor joints, cracks in floors or walls, expansion control cuts, gaps around service pipes. A self-leveling polyurethane caulk is recommended because it sinks in and fills gaps. The caulk also withstands hydrostatic pressure. Polyurethane caulk tends to remain flexible for years, even with settling and movement of concrete. It is recommended that wall/floor joints that have been covered with concrete be opened up with a grinder and the joint properly filled with caulk. (
Old 02-03-04, 07:53 AM
Visiting Guest
Posts: n/a
I'm not trying to make this look like a big project. We are in phase 1 (seal the cracks) before we do phase 2 (add the sump hole and pump system).

Our basement was tested and found 10 (whatever the measure is) which is not really much above the 4 so we could do nothing. But since my husband is a safety nut, and we plan on making a bedroom and family room (heavily used rooms) in the basement and we have a chance before we do the remodeling, we are going to mitigate.

So all I really needed to know was the type of caulk - now I know - self-leveling polyurethane. We are going to put the pump in ourselves (know how, can do, no contractor costs involved), I just wanted to know the type of caulk so I can start. No husband required to caulk.

Thanks both for the responses.
Old 02-03-04, 10:59 AM
Join Date: Mar 2003
Posts: 107
Upvotes: 0
Received 0 Upvotes on 0 Posts
Putting in a pump system is technically easy but do you know where you are going to put it and run the PVC pipe, and exhaust it above your roof line. You can not just put it anywhere. Do you know what your substrate is (under the concrete) is it 4-6" gravel with a vapor barrier which is good, allows the pump to draw air through the gravel, or is it gravel, dirt and what ever else our sloppy contrators left behind which impeeds airflow

I had mine professionally done at about $1000.00. After sealing everything up with a poly-calk they drilled about 8 or 9 small holes about 1" and then used smoke to determine air movement and best placement. My 4 year old house did not have the best substrate so we ended up needing two pvc pipes into the floor. Went from a 14.2 to a .6 Also the place I had wanted the pipe, would not have worked vey well.

My 2 Cents

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: