# Forum Home Renovation Demolition  Cutting Channel in Existing Slab for Plumbing

## thebionicwebste

Hi all, 
I've always enjoyed finding answers to my many renovating challenges on this site but I'm a bit stuck on this current one. 
We are putting an extension where there is an existing slab (that the engineer has certified) and looking to add an en-suite. 
I need to get the waste from the new en-suite to the existing waste. I'm keen to do the demo myself prior to getting the plumber in. 
My questions are:
1. Which location should I aim to open to join to existing waste (see Photo 2)?
2. How wide should I make the channel? Initially I was thinking just shovel width but if i need to put steel dowels in then I'll need it wide enough to get a hammer drill in.
3. Do I need to drill steel dowels from channel into existing slab prior to re-concreting?
4. Are there angles I need to know for the channel? Was thinking of coming out of new en-suite at 45deg and then a straight channel to the existing waste.
5. Any other advice/options? The only other idea i had was a macerator pump (to save channeling) but I've read mixed feedback on these. 
Photos and plan attached (excuse the mess). 
Thanks in advance for any help. 
Cheers

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## cyclic

Best attack is get a copy of existing sewer plan then get  Plumber on site to mark out and explain what is required

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## droog

Wow that looks like it would just about slice the slab in two ? I would be concerned with the potential structural impact. 
What's stopping running it outside ?

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## thebionicwebste

Yeah, I'm slightly concerned about that. Drafter didn't put the cut on the drawing the engineer signed off on. When i discussed with engineer he said it should be fine. Maybe I should throw some cash his way to do the analysis.  
That's why I was thinking the steel dowels would be a good idea to tie it all back together. 
Outside options are limited. The bed/WIR/en-suite wall is on the boundary. To go around the other way would be down path, across driveway, front yard and patio for a substantial distance.

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## johnc

Absolutely get the plumber in, you should be able to connect between the two rooms as well as only needing either 40mm or 50mm pipe for some of it. 
To drill for pins just run them on an angle and tap them down to level. Absolutely do not even think about runniing at shovel width. Pins simply stop the concrete patch from dropping, they don't hold together the Grand Canyon of trenches in a house slab. Your aim must be to trench for the bare minimum of digging

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