TV Coax cable next to building blocks truning black

[Michael Chare]

I have just replaced some TV coax which ran behind a U shaped plastic channel from my ground floor to my attic (2 storey house)

The downstairs wall is built using white bricks. The upstairs wall is built using a grey/blue block which has a finer texture and lighter colour than normal breeze block.

It would appear that the side (if you can have that for a round object) of the cable which touched the blocks has turned black, and the plastic sheathing is much more brittle than the cable which touched the bricks, some of which is like new.

This in itself has not been a problem and the cable worked fine, for the 25 years (or so) that it has been in place. It would appear to have a central copper conductor, but the outer braiding looks as if it could be aluminium. There was also a foil. The main reason for replacing the cable was that I wanted to run a CAT 5 cable next to it, and the easiest way of doing this was to use the old cable to pull through the two new ones.

What is worrying me is how many mains cables I have which are also next to these blocks and may be deteriorating in the same way. Is anyone aware of cables chemically reacting with building blocks?

[meow2222]

Your coax should have been black. Black coax is uv proofed and rated for outdoor use, the other colours arent.

PVC T&E can occasionally go brittle and fall apart outdoors, though it usually doesnt. The solution is to paint it with gloss paint. No undercoat, just gloss straight on. This uv proofs it.

NT

[Bill Wright]

Not with blocks. It reacts with polystyrene insulating blocks or chips. But who knows what the blocks were made of?

Bill

[Peter Crosland]

If it really is 25 years old it is long overdue for replacement anyway. As far as the mains wiring is concerned that is well overdue for professional testing in any case.

[john]

If the mains wiring is PVC then 25 years is nothing, it doesn't need replacing unless someone has damged it. If it's rubber then it will perish in time. So-called professional testing just involves an insulation test, nothing complex. If no fuses have blown or circuit breakers tripped then I wouldn't give a professional the invitation to make you feel you need a rewire.

[John]

Lightweight foamed fly ash based block possibly Thermalite?

Fixed wiring is not being moved to cause flaking off or detachment of the sheath so very unlikely to be a problem. Also mains cable is somewhat thicker and more robust than coax. AFAIK there is no identified problem for you to be concerned about but at twentyfive years old your installation perhaps ought to be inspected and tested.