Quick question - I know that PVC cable doesn't like polystyrene; something about the plasticiser leaching out and making the cable brittle - I've seen it happen - but what about expanding foam?
I've recently fitted a lot of flush-mount items in a 1890s/1900s terrace house which has random stone just beneath the black mortar & cement coat. Making the holes (what a job!) has left a lot of voids to fill which are going to take an awful lot of mortar or plaster or polyfilla, and I thought of small amounts of expanding foam.
Does anyone know if this stuff has any detrimental effects on PVC?
But isn't that low-expansion, high-density foam, as opposed to high-expansion, low-density foam. The difference is that the window isn't bowed as the foam expands, and rigid hold once set.
Whether chemically they're different I don't know. I guess though, if the normal stuff is used with PVC pipes through walls etc, then it should be okay.
Personally, I would run the cable through flat conduit, or fit cable protector over the cable if it is too late to fit conduit. That way, you don't need to worry about the effect on the cable of the materials you use. However, keep in mind that the better insulated a cable is, the lower its current carrying capacity, and check whether using foam would affect that. I would, however, have thought that a big bag of pink plaster would be a lot cheaper than the foam.
As someone else has already pointed out, uPVC windows and PVC as used in cable sheathing are different materials - you wouldn't want a window as flexible as a bit of T&E! Presumably this "plasticity" is due to the "plasticiser" which is not present in "unplasiticised" PVC. I'm not a chemist so don't have a clue about the details.
I only pointed out the plasticiser problem with polystyrene as an example of something already known - *if* there is a problem with expanding foam (I could get the proper name from the can, but it's elsewhere at the moment) it may or it may not be a plasticiser problem.
On the other hand there may be no problems at all.
While we're at it, what about Gripfill? Any solvent problems?
I take the point about derating the cable, but don't think it's an issue for this particular example. I'm intending only to use the foam to fill in a few of the larger gaps before levelling off with mortar and plaster or even polyfilla - the cable shouldn't be completely surrounded in foam, I'm just wondering about the odd point of contact. Fitting conduit was never really an option, and fitting a cap would be nigh on impossible given the uneven nature of the wall over which these cables are running.
If your only back filling a gap to prevent excessive use of plaster and there is no structural strength required. Whats wrong with packing the gaps with newspaper? The expanding foam won't have much structural strength either, at least not compared to mortar...
Newspaper is a thought for the deeper holes - it's getting it to stick to the vertical surfaces which is a problem. I suppose I could make papier mache...
Someone's going to come along in a minute and tell us we shouldn't stuff newspaper next to electrical cables for fire risk problems :-)
Well, sure there's a difference in the composition of the PVC for different uses, but it's presumably the same basic material? Also, I'd expect there to be warnings on foam if it did cause problems with cable, given the amount it's used these days.
What makes you think foam is polystyrene? It's nothing like the sort of polystyrene that causes problems with cables.
[sorry, I've had to re-arrange it in order to make replying easier - check Dave's original post if this is too confusing :-]
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Well yes, but as it is apparently the *plasticiser* which causes problems with polystyrene and that (AIUI) this plasticiser is only present in "PVC" and *not* "uPVC" then the difference is a vital one.
Fair enough. I just wondered if anyone'd come across anything. After all, there are no warnings on (for example) polystyrene coving and I've seen several examples of surface/conduit run cables coming through the ceiling and in intimate contact with the stuff.
I never said it was polystyrene. What I said was that there's a name on the can which I could post if I had the urge to fetch the darned thing to read it. If the can said "this is polystyrene" I think I'd have remembered it, and probably not asked the question in the first place.
Expanding foam is a horrid sticky, gluey stuff which is a pig to get off, discolours anything vaguely absorbent with which it has contact and degrades badly in sunlight. It just seemed like the sort of stuff which
*might* cause problems.
Since no-one has come up with anything I'll probably use it. It isn't going to be a lot anyway.
If you're that worried, wrap polythene sheet round the cable to act as a barrier. The plasticiser won't attack that -- witness the fact that any electrical product that comes packaged in polystyrene has the case (if plastic) and the mains flex protected by a polythene bag.
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