concretewire
I want to install fiber optic in my house. It shouldn't be an issue except at some point my phone cable goes through a 5cm-thick concrete slab that was cast around it. This happens in a weird corner which makes using heavy machinery difficult. My plan right now is to break the slab around the cable with a hammer and a chisel.
Is there a big risk to damage the phone wire? Is there an other way to proceed you recommend?
Your best bet for a good finish relies on doing three things:
The number and type of bars will vary depending on the load from the new shed but you should be fine with something like 8mm (3/8") bars at 200mm (8") centres.
You should probably note that this will give you a full structural connection and so may be too much for your particular problem unless you want to be absolutely sure that the slab and the extension don't separate.
We had an almost identical situation in a former garage that we refinished to be an office. Our contractor suggested this and we liked the result: he installed a piece of wood about an inch out from the concrete, putting insulation between them and keeping the wood a consistent and level height - a little higher than the concrete. I can't remember if it was pink fluffy insulation or spray stuff. Then a shelf about 6 inches out from the wall - nice and level by being a bit up from the concrete and supported by the vertical wood, and there's insulation under the shelf too. The whole thing is a good looking clear pine and is well varnished.
Looking from the side gives an idea of the distance from the wall:
The shelf runs around the entire room and is remarkably useful for something so low. It hides all the lumpy bumpy aspects of the concrete and while it's not something you see everywhere, no-one has ever mentioned it so it can't be that unusual.
Best Answer
If you need to maintain the existing phone cable, leave it alone. Actually, even if you're not planning on using the existing phone cable, just leave it alone.
If you want/need to run the fiber close to the existing cable, drill a new hole. That will give you a neat, tidy opening you can run the fiber through and shouldn't cause any damage to the existing cable, so long as you're not trying to get too close to it.
Optionally, run the fiber in a totally different location. Bring it to the slab, then run it up, in EMT or Schedule 80 PVC (for protection on the outside of the house), until you hit wood, then go in through the wood instead of through concrete. This will make all your work much easier as any work to get through wood is much easier than any method of getting through concrete.