Help! I am having my old cast-iron stack replaced with PVC so that I can add a third floor bathroom. The first and second floor toilet and tub connections were also replaced, with one problem.

We can't get the new drain for the second floor tub to seal properly. The tub is steel and the rim of the hole where the drain is supposed to seal is somewhat corroded. There is a small notch in one area and a small hole in another area. The old brass drain/overflow that was removed was obviously (green) corroded around the drain and I guess the corrosion was preventing a major leak. When we replaced it today with a new PVC drain/overflow, using only the normal rubber gasket on the bottom and plumbers putty on the top, it leaked like the proverbial sieve.

I have read in other threads (re shower drains) that using silicon gel (same as caulk?) on the rubber gasket sometimes does the trick. Does anyone think that will work? If so, would silicon gel/caulk on the top also help?

Another option I'm considering is trying to repair the steel itself with something like Bondo (car body putty?) Replacing the tub is kind of unthinkable at the moment because of the cost and disruption of having to replace not only the tub but the surround and the floor.

Any suggestions or advice are most welcome.

"Another option I'm considering is trying to repair the steel itself with something like Bondo (car body putty?)"

Repairing the holes and bad spots is a better idea then attempting to seal them with silicon jel.
Let me suggest another method. Instead of Bondo use Propoxy 20 made by the Hercules Chemical Company, Passic, NJ.
This is a steel reinforced epoxy putty that hardens like metal and can be painted,sanded, filled, drilled and tapped. This can be purchased at most hardware stores. Good luck, Tom

Thanks for your quick response, Tom. Good tip about the type of epoxy to use.

After looking at the tub more closely this morning, I decided that the edge deterioration is too bad to rely on epoxy alone, since it would have only a thin steel edge to bond to and would break off too easily.

I now plan to get/make a new steel shoe about 1/4" thick and just a little larger (O.D) than the flange and washer on the drain pipe so that I can have a good clean surface to mate to. I will sand/grind the tub surface clean and flat from the bottom, then bond the new shoe to it using the epoxy you suggest. Think that will work?

Bob B.

Hey Bob,
I don't know how it would work as a bonding agent. I've never used it for that purpose. I've never had to solder anything to a steel tub either. When they're that bad we just change them out. But good luck on what ever you decide. Tom

My plumber suggested that plastic would bond (with epoxy) just as easily as steel, and would probably be easier to fabricate. So today I modified a 3" Schedule 40 cleanout plug by cutting a 1 7/8' hole through the center and bonded it to the old shoe on the steel tub using 2-part epoxy paste. It's curing now and I plan to reattach the drain tomorrow. I'll let you know how it works out and maybe you can add another chapter to your "Tales of a Master Plumber."

My main logic for not replacing the tub at this time is that I would then have no working baths or showers for a house in which I have two tenants. I can see replacing the tub somewhere down the line, but meanwhile I have a new bathroom to finish first and replacing the tub (and surround, floor, etc.) would just slow me down. :)

Merry Xmas,
Bob