But how effective is Radonseal's formula vs. competitors? Radonseal's website doesn't point to any independent testing of its formula in relation to ASTM standards. I have seen posts claiming it is inferior to competitors--but again, no references. (It would be interesting to contact some of the institutional customers the Radonseal cites.)

But if all you have is dampness and humidity, that is normal for a basement during summer months. The only effective way to reduce that humidity--which should be less than 50%--is through mechanical dehumidification. There's no magic one-time wall coating that will remove humidity from the air.

As a builder, I have effectively used Permaquik crystalline waterproofing applied from the outside. It can be used on the inside too, but is best done by pros as it requires a pre-wash of the wall with sulphuric acid.