Finishing a basement

I want to finish my basement. It is an 80 year old house with a cynder block foundation. It doesn't flood or puddle, but in the warmer weather in Northeastern Massachusetts I need to keep a dehumidifier going to prevent the musty smell from creeping up - we also tested at 3.8 for radon - technically safe but a little high for my taste.

I've been hearing that I can lay down a vapor barrier of some sort before I lay down carpet or linoleum when I finish the basement and that this will prevent moisture and can reduce radon in the basement. I've heard about liquid coatings that sit on the surface, some that penetrate or simply using a "plastic sheet" first. What is the best one to use? What really works and is worth the investment?

[stevea]

I would recommend that you consider have Thermal Dry installed over your existing concrete floor. I would not recommend a liquid application but rather a sub-flooring membrane which is rolled out over the floor and then 1/2 plywood is placed on top and mechanically fastened to the concrete floor. You would then be able to carpet.
However it would be good to have a professional look at the basement and make other recommendations. I would also recommend that you look into a product we have called SaniDry which is a Basement Air System. I wouldn't recommend a finished basement without a SaniDry.