Plumbing Question

Advice on drilling old cast iron stack

I'm planning to connect a kitchen waste run into an old (~100 years) 80mm cast iron stack.

As the connection point required is a joist level, it's not possible to cut out a section and replace with plastic, so I'm thinking of drilling with a metal hole saw and fitting a boss for the new connection.

How realistic is this? Any advice on how to tackle this without damaging the stack?

5 Answers

Best Answer

hi i do a lot of work for a bathroom fitting company in my area and drill cast soil stacks on a regular basis.Diamond tipped core cutters do the job no prob just change masonary guide drill bit to metal drill bit.

Answered 26th Apr 2011

total residential property services

Member since 17 Dec 2008

You can drill a hole in cast iron, but you will need some good bits and hole cutter.
I really cant see you will get a perfect water tight seal to the cast iron.
You say its not possible to cut out the cast iron, I would imagine you can, and it would be a far better option.

I will give you the definition of impossible;

if you saw a bull in a field, thats not impossible,
if you saw a thistle in a field, thats not impossible,
if you saw a lark in a field, thats not impossible,

But if you saw a Bull sitting on a thistle, singing like a Lark; Thats Impossible.

Answered 24th Apr 2011


Member since 29 Oct 2008

you can drill the hole using power drill but you need hole saw which are purpously made to drill in hard metal.
But i sugest you change the stack for plastic one because it is easy to drill holes and you can fit a boss on stack and glue th boss with solvent cement.

I hope this info will help you
regards Leo

Answered 24th Apr 2011

L.P.P Leo Prendi Plumbing

Member since 15 Jun 2010

No feedback

You can buy a saddle to clamp onto the cast stack but they are expensive. Oxyacetylene can cut a hole in your stack bprior to this but as the other guys said its not an easy option. Replace the stack, plastic 100mm isnt expensive, removing the cats stack is a 2 man job as its heavy.....beware

Answered 25th Apr 2011

Jeff Stockdale Plumbing and Heating

Member since 28 Nov 2010

You will not be able to get a boss to fit on the cast iron stack due to the thickness differences between cast and UPVc but you should use some bosch or similar bi-metal cutters on a slow speed just slightly bugger than the external diameter of the pipe your looking at using to go into the stack and silicone it in place..

It's not ideal but is definitely the cheapest option!!

Thanks Daniel Lewis

Answered 25th Apr 2011


Member since 13 Feb 2009

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