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Drilling a Hole in a Cast Iron Tub

rbenjohnston1's picture

I have a large cast iron tub sunk into about 3 inches of concrete in an old building that I am working on. It's not going to be taken out or moved. The previous overflow valve has been epoxied over and the previous drain pipe is rotted through. The wet wall is open and I need to drill a hole through the tube to put in another overflow valve. I know this is not recommended by the manufacturer, but given I'm not taking out the tub, and that the tub is close to 90 years old I doubt I the manufacturer is still around. I really don't have a choice but to drill hole for the overflow valve in a 90 year old cast iron porcelain tub, does anyone out there have any suggestions?
Appreciate it in advance.
PS. The guy actually doing the work is a real tradesman but has not had to ever drill through a porcelain cast iron tub before. He's too busy actually working rehabbing the bathroom right now to post, so I'm the guy putting it out there.

(post #81766, reply #1 of 7)

Welcome to Breaktime.

(Rez, I'm taking your job)

There's a usually good search feature here. See the 'Advanced Search' in the upper left of your screen.

And there was just a thread about drilling cast iron recently.

'Man who say it cannot be done should not interrupt man doing it' ~ Chinese proverb

'Man who say it cannot be done should not interrupt man doing it' ~ Chinese proverb

(post #81766, reply #2 of 7)

  You don't want to drill. What you need is an abrasive hole saw to "grind" your way thru.

  Any plumbing supply house should have what you need.


(post #81766, reply #3 of 7)

You need to chip off the enamel first. Then use a hole saw.

(post #81766, reply #4 of 7)

I've got a set of Klein hole saws that will do the trick nicely. They're called Great White and they're carbide grit.

The local rental shop has these as well, I have no idea what they'd go for for a half-day rental.

There are 10 kinds of people in this world; those who understand binary and those who do not.

(post #81766, reply #5 of 7)

Grinding your way through witha hole saw is the way to go. As others have mentioned.

______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers

(post #81766, reply #6 of 7)

I had a client ask me to drill a hole in her granite countertop (and the cast iron sink flange) for an additional plumbing fixture. A diamond core drill worked fine but the porcelain coating did flake off a little. Fortunately the caulk joint sealing the sink to the countertop hid the area where the flake came off but I expect there may be rust stains bleeding through the caulk by now.

You can buy 1 3/8 diamond core drills as cheap as forty bucks. The two inch ones are closer to a hundred bucks.


(post #81766, reply #7 of 7)

I did to a sink not to long ago, was two hole, two faucet ( separate hot and cold fasucets), old cast about the same age as the tub. Went to a two handle one spout.

1. First a 1/4 carbide bit through the porcelain till you hit steel
2. Switch to a !/4 HSS bit to get through the cast iron
3. Used a carbide hole saw through the porcelain I happened to have one .
4. Standard Bi metal hole saw through the cast

But I was only doing a 1 1/4" hole I did not need much to get the spout in. Took some time and a 1/2 drill. Kept water on it to keep the porcelain and iron cool. You may need to grind the back of the tub flat to get a good seal with the overflow. It worked for me,