I have a 9 yr old house with a concrete slab foundation. On the first floor, the shower is on an outside wall. I am noticing what appears to be moisture on the outside, at the brick line down into the foundation. It is in a triangular pattern pointing down. Therefore I don't think it is coming from the ground up. I check it before taking a shower and no moisture is present. I take it afterwards and the moisture appears on the foundation. I have heard that fiberglass shower pans can leak, but I don't know how. I don't see any cracks and the chaulking appears OK. Before a plumber assesses it, can anybody let me know other ways it can leak? I'd like to be educated before having a plumber out. Thanks.

Do you have a tile shower or a manufactured shower enclosure?
Let's locate the source. Remove the strainer and blow up a balloon and tie it off in the drain or jam some wetr rags down the drain to close it off. Run a inch or so of water in the pan and let it set. Did moisture show up? Let me know. Good luck, Tom

Thanks for the suggestion. This is a fiberglass style pan, not a tile pan. After further testing it appears that my caulking around the base of the pan and tile wall was the problem. While I thought the small cracks were not a problem, I recaulked and ran the shower for an extended period. This appears to have fixed the problem. I've spoken with a few others and apparently even small cracks in grout/caulking can cause a problem. I'll continue to monitor it. Thanks again.