Wierd Shower drain problem

I am not a plumber, but I am mechanically pretty good. I have a situation with my shower drain that has me stumped, so I am turing to this newsgroup. The shower in question is a fiberglass Aquaglass shower stall, 1 piece. The base is solid. Here's the story:
THe shower drain started leaking. The drywall below the shower was damaged, so I cut out the drywall and found that 4 years ago when the house was built, the plumber did not glue the drain to the PVC pipe. The drain is similiar to this one:
http://www.oatey.com/apps/catalog/showskus.asp?ctg &subctg=4&prodgrpid3
Obviously a little luck, and the tapered fitting must have made it last 4 years.
I called a local plumbing company (good reputation) and the plumber that arrived took the drain apart and glued it like it should have been. I wanted to give it a little time before I re-drywalled just to make sure it was not going to leak anymore. I also marked the drain nut (the nut that holds the drain to the shower base) to see if it was going to back off. He tested the drain before he left and it did not leak. About a week later, I thought I noticed some water around the drain nut. So, I stopped up the drain with a 2" test plug, filled the shower and it did leak. More of a seep, but close to dripping slowly. This was with my wife wading through the water in the shower. It did seep without her in it also. The drain nut marks indicated that the nut had NOT moved.
Called plumbing company, so they sent over a very experienced plumber to look at it. He cut the PVC and pulled the drain out. Replaced the drain with the same style, and used one of those no-hub connectors, it did have the stainless steel jacket. Before he did that, we both looked for any cracks in the fiberglass around the drain. We couldn't find any. I saw that he put a good amount of putty around the flange before he wrenched the drain nut down. We tested it, no leaks. I marked the drain nut again. Later that night, I did the test plug deal again with my wife, no leaks.
This brings me to last night which was about 2 weeks since the last plumber. I tested it again, because I was going to re-drywall. I did the test plug deal again, and it leaked/seeped like the first time. THe drain nut marks again indicated that the nut had NOT moved.
Now to today. Before I loosened the drain nut, I checked to see how tight it was. I felt right at the line of snug. I loosened the drain nut, and loosened the no-hub, pulled the drain up. I looked for an hour with a magnifier and bright light, and could find no cracks at all. In fact the drain part of the base looked in excellent condition. So, I installed a brass drain like this one:
http://www.oatey.com/apps/catalog/showskus.asp?ctg &subctg=4&prodgrpid8
I used a good amount of putty, and tightened down the drain nut, reconnected the no-hub. It is not leaking at the moment. I do have a very good fiberglass guy coming to look at it next week. Just in case I missed something with the fiberglass part. I can't help thinking this drain will start leaking in a week or two. All of the leaking that I have noticed with this drain seems to be coming from between the shower stall and the rubber gasket, bottom side of shower. So, my questions are:
1. How tight should a shower drain nut be?
2. I know this is out there, but I have to ask. Do these drains have issues with expansion/contractions problems, at least when they are first installed?
3. Could the putty settle more in a week or two?
Any insight is appreciated.
Thanks,
John
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Since you have the underside exposed, have your wife walk around in the shower while you are looking at the underside. The drain seal may be failing because of too much flexing of the shower base. If it's flexing, then you will need to support the underside better (expanding foam usually works well for this).
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I'm guessing that over a week's time, the base of the shower if flexing and damaging the seal. Can you better support the base? Instead of putty, perhaps silicone caulk would be better. Ed
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If memory serves, the products that the shower is made from exhibit what is called 'cold flow'. i.e., when you tighten a not/bolt configuration around this material the pressure will cause it to migrate out/away from the pressure.
As such, the primary sealing in this joint needs to come from some sort of bonding agent. I think the post above re silicone caulk is on the right track.
It seems like there should be easy answers to this since there is nothing unusual about your configuration. It seems like the culprit would have to be the shower base being too flexible which does lead to the issue of whether there are already small cracks that you haven't yet dicovered that either (or both) resulted from too much flex or even contribute to too much flex.
In my town, the Home Depot I go to has an ex-plumber in the plumbing department that I can pose questions to. If you know of a plumbing supply house, you can go ther and ask but the best time to go is about 9:30-10AM. Don't go there when there are a lot of licensed plumbers around (like the first part of the day when they are there getting materials for their trucks or their first call). The staff will sometimes be a little heinky about helping you much in front of them. OTOH, sometimes the people around will overhear and toss out suggestions. I think some of it depends on how strong unions are where you live.
I thought the idea of a hard polyurethane foam was an interesting idea (and possibly the only 'effective' one for flex) but that tends to make any of your solutions **extremely** difficult to revisit and given that you have drywall underneath you'd probably have to be putting in some sort of (removeable) cross-member between the two relevant joists that you'd need to have not be flush with the drywall (to accommodate flex in this member and avoid it popping your new ceiling drywall joints). blah-blah-blah...
G*d*mn I hate plastic things - especially in plumbing. With the exception of PVC tubing/piping, it always fails. I have not even used PVC on supply lines because I am suspicious of it. I am still using steel and copper for that. I would feel comfortable with PVC supply lines only after seeing this stuff in service for another 30 years or so. It is amazing that there is nothing in plumbing (or many other disciplines) that some *ssw*pe won't try to make out of plastic.
The problem is what people consider to be 'serviceable lifetime'. 'Contractors/remodelers/investors' only need 6 months to a year to get the unit sold. Even homeowners don't need long because nobody seems to live anywhere for longer than 5 years. My house is 85 years old and I am planning/hoping to live here at least another 30 years. I want my repairs to **last**.
What a PITA problem! Good luck. Let us know what eventually works.
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My two cents: Ultraviolet light is pretty good for highlighting cracks in fiberglass and acrylic showers. They glow.
Good luck.
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I had the same problem with a shower stall that I was fixing for a friend except I was so confident that my work would hold that I put the drywall back in. It didn't. What I finally did was use silicone seal instead of putty. I found that the movement of the shower floor caused the putty to work loose. Hasn't leaked in over a year.
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Comments about the possibility of the shower base flexing being the primary source of the problem is very likely. The leaking drain might actually be a "result", not a primary.cause of the leak. As suggested, get a can of foam and get it under your base to take up any and all spaces. Let it expand out and when cured trim as necessary. Foam was recommended by the Shower manufacturer that I have and solidified a flexing shower pan. MLD

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