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.

Stopping water entry from the inside of a foundation does nothing to stop water damage inside the wall and under the footings. As for radon, even if a water-based sealant could seal every visible crack and crevice it will miss the many other entryways into the basement for an invisible, odour free gas, such as drains, voids in blocks, water-lines. Here is a link that might be useful: Radon mitigation systems

So the fans seem to work? I had been interested in the sealers as well because our basement developed some mildew after we moved in--but I read somewhere that they stop working and that you need to re-apply. Is this true? I will check if there is a code for radon fans here. Have you had your level checked since you had the fan installed? The radon really bothers me. I hope that we haven't lived here long enough for it to have hurt the kids. We did not have our own agent when we bought our house and the seller's agent said "as a science teacher, I can tell you that you have nothing to worry about with radon. It is an odourless gas that cannot hurt you and I think you should save money and not get the test." We got the test, but the results came in after we had made an offer. He was obviously knew the level was high and was not working in our best interest (although he took the cut as if he had been our agent too.) I can't imagine that the New York Realtor's association would condone that kind of talk about radon.

R408.3 Unvented crawl space. Ventilation openings in under-floor spaces specified in Sections R408.1 and R408.2 shall not be required where: 1. Exposed earth is covered with a continuous Class I vapor retarder. Joints of the vapor retarder shall overlap by 6 inches (152 mm) and shall be sealed or taped. The edges of the vapor retarder shall extend at least 6 inches (152 mm) up the stem wall and shall be attached and sealed to the stem wall or insulation; and 2. One of the following is provided for the under-floor space: 2.1. Continuously operated mechanical exhaust ventilation at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7m2) of crawlspace floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1103.2.1 of this code; 2.2. Conditioned air supply sized to deliver at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7 m2) of under-floor area, including a return air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2 of this code; 2.3. Plenum in existing structures complying with Section M1601.5, if under-floor space is used as a plenum. http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_4_sec008.htm