Currently have jute backed indoor/outdoor carpet glued on a 20 year old concrete basement floor rec. room with wood stove. Would love to replace it. One estimate suggested to lay new carpet (similar) on top of old carpet, using the old as underlay. The other estimate suggested we remove old carpet and glue and lay proper underlay and carpet. There is no sub floor and no fear of a wet basement, our house is sitting on bedrock. Obviously there is a wide price difference, but we want to do it properly.
Answer:
First find an environmentally friendly neutralizer so you can get rid of the old adhesive without having to worry about fumes and the like. After that, you should put in new carpet complete with underpad in your particular situation - no possible chance of moisture.