shower rebuild

[mecker]

I am currently rebuilding from a disasterous shower failure that rotted the entire bathroom subfloor. It was a fully tiled shower stall with durock backer and PVC floor membrane. It was done by a contractor and I found a razorblade cut in the membrane probably made while cutting the drain and few other violations of the proceedures I've been reading on this and other info sites. The original shower had failed in less than 10 years and the rebuilt one destroyed the bathroom floor in five years.
The shower walls are still good with tile over durock and I would like to keep them if possible and replace only the floor. I cut out the damaged PVC membrane which extended behind the backer. I can't get a new one behind there without tearing out the walls. I don't want another tile floor anyway for this basic reason:
You are depending on a moisture barrier which you cannot see hidden below the tile. If it fails, you don't know until your subfloor starts to cave in. Now I want to install a moulded plastic shower base so that the moisture barrier is the surface I'm standing on so if it fails I will see it.
My problem is joining the top flange of the shower base with the tile walls in a way that won't leak. I have read how this is done if you are building the walls from scratch over the base, but I want to keep my walls. The base is not a perfect fit. This is more of a problem than I thought it would be. I'm now considering custom building a base in-place with glass/epoxy (I'm a boatbuilder). I'm starting to think it might be easier to tear down the walls and start from scratch.
I would appreciate any advise.

[SeanP]

Did you also check to see if you had any leaks in pipes behind the wall.

If you are reusing the walls make sure there is a moisture barrier behind it.

I had a shower that was leaking and at first I thought it was the pan but it turned out to be a leak in the riser going to the shower head.

The shower was an absolute hack master piece.(greenboard walls, no moisture barrier, tiled with mastic, plastic shower drain with riser just stuffed into the cast iron p-trap, pvc membrane nailed in over the curb, no dam corners, made the shower head riser pipe out of two pieces of copper and didn't secure the elbow so moving the shower head caused the leak etc...)

With those plastic molded pans, I have seem them twice now in hotels where they have leaked at the drain flange and water has gotten under neath them.

I think the bottom line is that no matter what, it takes good workmanship to be succussful, regardless of the method used.

[Davestone]

Yes i've seen them leak too,but you could put one in,flange behind cbu silicone completely around drain and lip and see what happens,probably wouldn't hurt to totally waterproof underneath either.But if you use our method of pitch and pan testing it won't leak.