Can I use expanding foam in a gap in a timber joist that cables run through (i.e. in the circle in the picture below)?
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Expanding Foam around electric cables
- Thread starter spiidey
- Start date
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For ordinary foam no - because it can react badly with the pvc - it will say so on the can. The other issue is that the foam will form a heat barrier and this may weaken the outer sheath of the cable.
However, I believe there are some specialist foams that do allow you fill holes around cables without causing any problems.
However, I believe there are some specialist foams that do allow you fill holes around cables without causing any problems.
Why bother?
My understanding (confirmed by exchanges with manufactuer's in the past) is that that 'standard' (polyurethane) expanding foam is fine in contact with PVC cables - it's expanded polystyrene which is the problem with PVC cables. Am I wrong?
Indeed - and that is a good reason for not using foam of any sort. I can't really see why anyone would want to fill the gap (I presume the OP means the gap around the cables).
Kind Regards, John
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Yes why bother, if an issue silicon sealant will do!
Yes why bother? if an issue silicon sealant will do!
Fire rated foam is often used to fill holes where cables/cable tray etc pass through walls in commercial buildings, above suspended ceilings etc.
No idea why you would want to fill a hole like that though?
No idea why you would want to fill a hole like that though?
I would be a little more concerned with the distance between the underside of the joist and the hole. Should be at least 50mm.
... but a bit late to do anything about that!
As I presume must be true of others, I've seen some horrific situations of holes through, and notches in, joists in my time - some leaving precious little wood. However, has anyone ever heard of a floor collapsing as a result - I certainly haven't?
Kind Regards, John
Think it would need to be every joist butchered in pretty much the same place to cause any collapse....
Did see a Fire Alarm engineer stitch drilling a joist with a 20mm drill bit, making a hole around 100mm round for cables to feed through into a riser in a hotel. He left practically no wood! Site foreman not happy!
Did see a Fire Alarm engineer stitch drilling a joist with a 20mm drill bit, making a hole around 100mm round for cables to feed through into a riser in a hotel. He left practically no wood! Site foreman not happy!
50mm distance between underside of joist, has nothing to do with continued structural safety of joist!
"Mechanical damage" and have come across plenty of it!
I'm sure it would - but that, of course, is what people tend to do when then run pipes/cables across a line of joists.
You will probably recall seeing her a while ago pics of a line of joists which someone had 'notched' to take a 100mm soil pipe.
However, despite all these abominations, I haven't heard of a resultant floor collapse.
Kind Regards, John
I realise that (up to a point, although it obvioulsy does have an impact on structural strength/safety) - although the person who made that rule obviously hadn't seen my collection of nails and drills - many of them plenty long enough to get a cable far more than 50mm in
... it was just your mention of holes in joists which made me think of that question!Kind Regards, John
Not a great deal to say about that, other than crack on!although the person who made that rule obviously hadn't seen my collection of nails and drills - many of them plenty long enough to get a cable far more than 50mm in
Don't the regulations about burying cables and drilling joists with a 50mm. rule automatically and obviously mean screws and nails longer than 50mm. should not be used?
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