RadonSeal - Any Experiences?

benbrewMarch 30, 2006

I am looking to do some basement renovation to create an in-law space downstairs....however, I've got a radon problem to deal with first! I'm not too keen on the fan-based mitigation as I would then have to work around it. So, the spray on product, Radon-Seal, looks like it could really be great:


Unfortunately, my basement floor has been painted, so I would first need to strip the paint and then apply the product. This will take a ton of my time, so I'm curious to hear if anybody out there has used, or is considered using, this product and would be willing to give some feedback...


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I used RadonSeal on my basement walls, and am 3/4 done appying it to the floor.

I was skeptical before I ordered it, and am still a bit skeptical, here is my experience:

When the home was inspected, the radon test came back at 6. Several months later, I tested it myself, and it came back at 7. I sealed the gap between the slab and the walls with self leveling polyurethane caulk, applied RadonSeal to the walls, and painted the walls with UGL DryLok latex paint. The next test came back at 1.

So, I did more than apply the RadonSeal, so it's hard to say how much each action helped.

The RadonSeal was easy to apply, and it soaked right in as advertised. It really is odorless, and it feels slippery, I suppose because of some surfactant. The overspray dries into clear crystals. The web site claims that the Silica based stuff in RadonSeal reacts with the unincorporated lime in the concrete. I've been meaning to mix a bit of RadonSeal with lime to see what happens, but haven't done it yet.

My floor was painted as well, but it was not a good job. Water soaked in, and where it was wet, you could see a network of cracks in the paint. I have been stripping the floor a section at a time with a belt sander, which is really unpleasant work, but I do not want to use a chemical stripper. After stripping, I'm applying RadonSeal, then painting.

So in the end, it's hard to tell how much the RadonSeal helps. I do know that I only want to do this once, so I'm doing everything I can to ensure that moisture and radon won't get in. I will say this; the company has been around since at least 1995, and I couldn't find a single complaint about them on the web.

Fortunately, my basement walls and floor are in good shape to start with, only one visible crack in the floor. If your floor is riddled with cracks, I think it will be difficult to seal out the radon.


    Bookmark   April 5, 2006 at 11:50PM
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Thanks much for the detailed reply...hadn't checked back for a while, so was thrilled to see it. It sounds like I'm in a roughly comparable position. My radon readings have been about the same as yours. Our basement, from what I have seen thus far, really has no water problems and the floor and walls are in great shape. No big cracks of any sort, etc. It's interesting you had such a big drop in radon just by doing the walls and sealing the wall/slab junction. From Radonseal's website, they would argue that doing the floor is often the most productive.
Our walls are painted concrete block, so I would have to strip those as well. Are your walls block? Or poured concrete?

    Bookmark   April 13, 2006 at 11:07AM
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radon gas will take the path of least resistance and if your floor has no cracks in it then radon will enter through the junction created at the floor/wall. Thus its not suprising that sealing this joint will greatly reduce the Radon level....I am curious why he used BOTH radonseal AND UGL DryLock as radonseal claims it to be effective as both a radon and water sealer in one and I know these aren't cheap products....but glad it seems to have worked for him

    Bookmark   April 14, 2006 at 10:53AM
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Anyone use just RadonSeal without any supplemental coatings??? how effective is it for waterproofing? they claim it to be a solve all for water and radon...all test conditions being equal if it stops/slows radon (a gas) it must stop/slow water even more. can anyone confirm or deny RadonSeals efficacy at radon AND water inhibition???


    Bookmark   April 18, 2006 at 2:25PM
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When I bought my house (northern NJ) a few years ago I have a radon reading of 6 in the basement. I had a contactor install the subslab ventilation system and now the reading is 1. I would like to get it even lower and am considering sealing the concreate floor and block walls. The product I found is called SANITRED. It is primarily used as a waterproofing seal but the manufacturer claims it prevents radon from entering as well. But I would need to strip the existing paint from the walls and floor before application.

Maybe I'll start with the floor/wall junction and see what happens.

    Bookmark   April 26, 2006 at 10:39PM
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hello fellow NJersey-ite!! I'm in Central NJ and have a much higer reading than you did....I looked into ALL the sealants, RADONSEAL, Thoroseal, Sanitred, DryLock etc....If I remember right that sanitred sealant is super expensive polyurethane product!!!! any recommendations you received for this product...anyone in NJ use it and have results???

    Bookmark   April 27, 2006 at 2:57PM
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My walls are poured concrete, except for a ~7 foot section below the fireplace whiich is block.


I used both mostly because I couldn't be sure how either would perform. If they both work, great. The Radonseal should be a permanent seal, and the walls look much better after being painted white with the drylock.


    Bookmark   April 29, 2006 at 12:17AM
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Sani-Tred isn't as expensive as you make it sound. Poured concrete requires 2 coat of PermaFlex which costs approx $00.76 per square ft.

Cement block is extremely porous, it requires 3 coats of PermaFlex which costs approx $01.14 per sq'

Most all basements have a cold joint where the wall meets the floor. Some have other joints, cracks or holes. These areas just need a little LRB/TAV mixture (Liquid Rubber Base, Thickening Activator).

I contacted radonseal and asked for some technical info. I received 2 PDF files. This is what EVERYONE should be concerned with  the tech data. Do not pay attention to the advertising hype, just the cold hard facts.

Radonseal Test Results:

ASTM-C-67 Section 13
Results: Up to 35% decrease in absorption transmission

In other words it MAY reduce water/radon in your basement by MAXIMUM of 35%. Does this meet your expectations? That is the real question.

ASTM-C-67 Section 25
Results: 35% decrease in suction.

This means that in comparison to using Sani-Tred as a 100% seal of all water, moisture, vapor and radon  Radonseal will leak by 65%. It would be reasonable to derive from their claims that Radonseal is a sure failure if it can only make your basement 35% more waterproof than it already is.

ASTM-C-67 Section 29
Results: Significant resistance to efflorescence (plus 50%)

Efflorescence is the minerals left behind AFTER the water/moisture has already entered your basement. If Radonseal will ONLY reduce efflorescence by 50% Â it is reasonable to assume that Radonseal WILL NOT, CAN NOT waterproof or radonproof your basement to anyoneÂs expectations.

Results: Significant improvement in curing against hairline and spot drying.
ORF Method Resistance To Dusting
Results: 100% improvement against dusting due to abrasion.

Who Cares? Anyone ÂAnyone?

ORF Method Resistance To Dusting
Results: 100% improvement against dusting due to abrasion.

So what ÂSo will any paint, what truly matters is will it waterproof, moisture-proof, vapor proof and STOP radon in its tracks? Obviously NOT Â read their own tech data.

ASTM-C-666 Using 5% NaCl
Results: Improves resistance to salt attack during freeze/thaw conditions in the presence of moisture.

Whooptidy Doo!

(Surface coat only)
Results: +15% at 8 days.
+23% at 31 days.
+42% at 90 days.

    Bookmark   January 17, 2007 at 2:55PM
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I built new and first used drylok on the walls, both outside and inside. Totally sealed and the white paint looked nice on the brick walls for moving into. Yes, the outside was treated with standard tar afterwards as well. After moving in the Radon test was at 4.6. I then used Radon-Seal on the floors which dropped it down to a 1.4 when I tested it 3 weeks later. Two coats went down. Lastly I applied an epoxy finish on the floor to give it some type of texture unil I finish off the basement. That did not reduce the Radon any further. Then only drawback I saw with the Radon-seal was that if I spilled water on the floor, like from the dehumidifier, and did not wipe it up right away it seeped through the epoxy but not through the Radon-seal. Which then caused the epoxy to bubble and seperate from the floor. So obviously its a great water sealent. To reduce the radon any more I'm considering sealing and venting the sump crock to the outside and if need be use the SANITRED around the perimeter where the walls meet the floor. They sell a compound that is thicker that can be poured in the crevice like a latext caulk. If I had to do it over again I would use the Radon-seal on the walls. Drylok was cheaper, but Radon-seal was much easier to apply using a garden sprayer then trying to get a heavy duty paint sprayer to pump that thick drylok paint. The actual radon levels are probably a lot lower in the basement anyway since we rarely keep it air tight for long periods. I have my workout equipment down there and always crack open the patio door (exposed basement in the back) when down there every day for 1 hour.

I also turned a friend onto Radon-seal. His was over 7. He did 1/2 the basement and dropped it to a 4. Then he had to rip up the carpet and do the other half. Highest readings were near the sump, so he sealed and put in a power vent. Now he's under a 2. Where he lives the area is known for high radon levels and he was unaware of the issue until I told him of all the stuff I was doing for my place since being new it was all open and the time to do it.

    Bookmark   February 10, 2007 at 3:19AM
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Thanks for all this information. We are in process of building a new house in central valley, Calif. and I insisted on a basement. I discovered about radon problem and am using RadonSeal as soon as cement floor cures. One question I have is, does having a door open to outside patio help the radon escape? Also does a gas fireplace do anything about radon?

    Bookmark   February 23, 2007 at 1:41AM
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Given that the testing procedure requires that one keep windows closed and minimize the usage of doors, it seems that ventilation of any sort will reduce radon concentration. That said, radon density is about 8x of the earth's atmosphere, so it's not going to automagically find its way up your chimney. I'm currently building a workout room in my basement and am seriously considering adding a fan vent.

    Bookmark   April 6, 2008 at 8:59PM
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Be aware that radon levels vary...you can test today and get 1.0 pCi/LÂ..and next week or next month get a reading of 6.0 or higher....so although sealing cracks, etc is a good adjunct to a mitigation system, it is not the best sole method to use if one wishes to be assured that the radon level stays below the recommended minimum of 4.0 pCi/L.

The EPA recommended mitigation for radon is indeed a mitigation system with a fan...as one can be assured that the radon will continue to be reduced unless the fan stops working...which saves a lot of testing. Any other method will require periodic testing to make certain the level remains below 4.0 pCi/L.

Here is a link that might be useful: A Citizens Guide To Radon

    Bookmark   August 9, 2008 at 2:35PM
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Worthless product. Bought it as more of a waterproofer even though I have radon and after applying it per directions, we had dry weather for a good 2 weeks here in MN and then the first rain, my block walls were wet again. If it can't keep the big water molecules out, double it could keep a gas out.
Save yourself $200

    Bookmark   September 11, 2008 at 3:01PM
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Basement waterproofing materials can vary significantly in their forms and their uses. Some will be available to the public and some may only be available to the trade. Let's take a look at what is around and how you can apply it to your home situation.

First of all though, you need to be aware that the area you live in also affects the amount of water that's likely to be around. So take that into consideration as this will also influence the type of materials you can use.

    Bookmark   April 30, 2009 at 1:03AM
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Used RadonSeal in my basement in summer of 09. Personally, it has worked as expected. Much less humid down there!

    Bookmark   February 3, 2011 at 1:23PM
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"The EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently." EPA

Here is a link that might be useful: EPA Consumer's Guide to Radon Reduction

    Bookmark   February 5, 2011 at 2:56PM
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Our CT home was built in 1852. We have granite foundation walls. Just got a short radon test back of 5.4. We just dug out our basement (was formerly a dirt floor), and installed a 10 mill poly vapor barrier under a newly poured 4,000 psi, 4" concrete slab. Was hoping the vapor barrier alone would reduce the radon, but I guess not. What I'm curious about is should I attempt to seal the granite block walls, or should I do an active underslab vent first?

    Bookmark   March 8, 2011 at 10:18PM
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