March 2nd 2009. I applied Radon Seal per the instructions on the container. My results were no difference in radon readings. This is very disappointing.
Details: I live in Colorado just outside of Boulder, radon is an issue with many households here. I first measured my radon using a mail-in capsule a couple years ago. My readings were about 9.5. As a result of this I sealed all if the expansion joints in my basement (with a floor leveling product) and re-measured. New readings were ~2.5. So roughly a 75% improvement. This was during the Summer of 2007 so seasonal variations should not have been a factor.
I read that radon levels can vary based on the season and Winter levels are typically worse due the frozen ground and lack of airflow so I recently bought a digital radon meter. I measured using this meter about 2 months ago. Unfortunately my Winter readings were about 10. I then found RadonSeal on the internet. I only read a couple bad reviews so decided to risk the purchase. None of the reviews were very controlled, those with the best reviews also sealed their expansion joints etc. at the same time they applied the product. Since my expansion joints were already sealed, my readings should accurately reveal the results of Radon Seal I followed the application instructions to the letter and applied 3 coats of Radon Seal. I applied it to the floor and ~2 feet up the wall over the entire basement. I have a walkout basement so the concrete walls are limited. My readings before applying radon seal were from about 9.5 to 10.5 pcl. My readings after applying Radon seal are also 9.5 to 10.5. In other words the benefits of Radon Seal were zero.
Based on these results, I view RadonSeal as worthless. I contacted the manufacturer (they supposedly guarentee their product) but all I got were a bunch of excuses. I still have ~ 2 gallons left and would be happy to sell it to someone......