It's well established that polystyrene (thermal insulation, for
example) isn't supposed to touch PVC cable. But I was surprised to be
advised here a while ago by someone reliable that it's OK to put gloss
paint on it (I'd always assumed the solvent would be bad for the
insulation). And it's nice to know that Sharpies are OK.
Is there a definitive list of things (within reason, that is,
particularly things like types of thermal insulation that you might
put there without realizing it) that aren't supposed to touch PVC
cable? Are there any other surprising things that can touch it?
Polystyrene isn't much of a problem.
It reacts with the plasticiser to make the PVC less flexible but the
plasticiser causes the polystyrene to shrink.
Once its shrunk enough to create a gap the problem has gone away.
Except if the polystyrene is in the form of loose beads in which case it
may just move down onto the cable.
But as you say, if the cable is not subject to movement, you might never
find out its a problem... Not that you should ever knowingly do it of
Not aware of any. Sharpies do have a solvent in, but mostly leave
pigment behind which is harmless.
You would maybe consider gloss paint to be a danger item, but people
have been painting (and varnishing) cables forever without obvious issue.
Polystyrene is a rather non obvious and fairly special case. Perhaps
might never have been noticed except for cavity wall insulation.
Oil based gloss paint will dissolve into the surface and carry the
paint pigment in, but it doesn't go far enough in to do any harm.
Because the paint pigment is dissolved into the PVC surface, it
won't ever flake off. You use top coat only (no undercoat is
needed because top coat binds directly).
(Same is true for gloss paint on PVC window frames, PVC waste pipes,
I have not tried this using the current low volatiles gloss.
I did come across some T&E cable clips made from polystyrene. Each
one looked like it had slightly melted onto the cable, and at a
first glance, I thought the cable might have melted at some stage,
but it hadn't.
I don't know of any list, and neither the paint nor the cable
manufacturers will tell you it's safe to paint the cable with
gloss paint. Dried gloss paint is more flammable than PVC, so
there may be some situations where it's not advisable.
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Eventually it will go through and find somewhere polystyrene free to
rest or hang.
Maybe someone can get a polystyrene tile and some PVC cable and setup a
webcam. It would be better than the watching paint dry ones.
As an example, just unpacked the old BBC micro to pass it on, it has
been sitting in its original PS foam packaging for 15(?) years or so at
normal room temperature. Where the PVC mains lead was pressed up
against the foam polystyrene packaging it has gone all sticky. It seems
that the platicisers leaching out of the PVC had turned the PS into a
sticky goo a bit like printers' snot but could be peeled off the cable
leaving it more or less unmarked.
I think with paint it depends on the base of the paint, but one issue is
that it never seems to dry well on pvc, it goes tacky.
Make sure it does not get too hot of course, and from experience hot and
cold cycling or exposure to sun for long periods does not do it much good
either, though I guess it depends on the quality, something you have to take
From the Sofa of Brian Gaff Reply address is active
"Adam Funk" < email@example.com> wrote in message
While agreeing that PVC cables and polystyrene should be kept apart I don't
think the potential risk is very high.
Recent work in my house revealed that we had 2 inches of polystyrene behind
the plasterboard in most of our rooms. PVC cables were run behind the
polystyrene without any protection and did show some sign of hardening on
the surface but not enough to cause any problem. The cables and polystyrene
have been there for at least 10 years, possibly nearer 20.
I certainly don't feel any need to replace all the existing cables though I
did make sure that the additional cable I installed for the extra sockets
was well separated from any polystyrene.
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