||08-18-2008 10:03 AM
I plug every plumbing fixture penetration with expanding foam sealant, I'll take the opposite view and say fiberglass isn't the way to go. It is terrible at stopping air flow, and shouldn't be for sealing air leaks and in a moist environment is particularly a bad choice it turns into a mold/mildew breeding ground. I think stuffing it with fiberglass just isn't the way to go, it doesn't stop air flow, and with cold air flowing through it moisture can condense and I think installed at your shower drain attempting to stop air flow, instead you will create an environment for mold/mildew.
I would use expanding sealant around the floor penetraion (not shower drain) and let it expand and seal. Practice with it if you've not used it before it will expand about 3x-4x larger than when you first apply so leave it room to expand or if there isn't much room only use a small bead. If you judge wrong and it doesn't expand enough to seal the opening, you can always apply it again to finish the job which is much better than putting too much, which causes it to expand uncontrollably out every crack and it will just keep coming... it's better to be safe than sorry and put too little and another application if necessary. The cans have to be used upside down, nail polish remover can remove accidents while still wet but once dry it requires elbow grease. If possible try to seal the floor penetration from below to minimize it interfering with your shower drain. Expanding sealant is approved for wet conditions, impossible for mold/mildew to grow, and for sealing air leaks so it's the right tool for the job however it's also permanent as it dries solid and sticky as crazy glue the only way to remove it once dry is with a razor/knife.