Help: conduit duct into loft has condensation

[j_s]

Hi guys, I've got some 40mm conduit that carries aerial and cat 5 cables from one bedroom (office) up to loft and then the cat5 continues down into another bedroom stud wall and down to the lounge via another 40mm conduit. Conduit does not connect between the 2 points. I use pro clima stoppas to seal end of conduit and the cables go through the stoppas and it's meant to seal it.  Issue I have as the stoppa on the office end in the loft isn't sealing around the cables very well and warm moist air is coming up the conduit and then some condensation is forming near the end of the conduit. 

 

I've put some expanding foam in the conduit ( allowing a gap for the stoppa still) last night but it's not completely sealing it still. If I tape up the end will this stop the condensation as long as it's buried under at least 200mm of dense wool (I'm using dri therm 32).

 

I can't get to the other end of the conduit now as it's within a just recently redone stud wall but I am taping up and foaming any gaps in the sockets and will seal the stud wall under it too with tape and whatever I can find. The bottom of the stud wall is open for the mvhr ducting to get down to the lounge and dining room so I'll have to find something to seal that as it is a large air path to the open end of the 40mm conduit 

 

Thanks

James

[ToughButterCup]

3 minutes ago, j_s said:

[...]

Issue I have as the stoppa on the office end in the loft isn't sealing around the cables very well and warm moist air is coming up the conduit and then some condensation is forming near the end of the conduit. 

[...]

 

Is that the question? How do I make sure there is no warm moist air in the conduit?

[Jeremy Harris]

I found that wrapping individual cables with a thin layer of self-amalgamating tape close to where they come out of a conduit, then wrapping self-amalgamating tape around the end of the conduit and stretching it to form a membrane over the end and then continuing to wrap it around all the cables worked pretty well.  I did test for air leaks with a Testo probe airflow meter and didn't find any, so concluded that this method was pretty airtight.

[j_s]

54 minutes ago, recoveringacademic said:

 

Is that the question? How do I make sure there is no warm moist air in the conduit?

 

Sorry I should have actually asked the direct question. I suppose the question is, can I seal from the loft side as per Jeremy's reply or could that still cause issues even if conduit is buried within the loft insulation, or alternative is how to stop the warm moist air getting there in the first place. I'm not so sure I can stop it from getting there now.

 

Jeremy , you say self amalgamating tape, could you please give me an example? I use and have pro clima tescon, could I use that?

 

Edit, I understand what tape you mean now Jeremy. There is a cheap one at Screwfix (£2.50 made by Diall) or everbuild do a silicon based tape which is £11 

 

Any advice as to which to go for?

 

Many thanks

James

Edited November 29, 2018 by j_s

[Jeremy Harris]

The cheap stuff from Screwfix is fine.  Just remember that you have to stretch it as you wrap it around anything, as stretching it causes it to self-amalgamate.  It's not sticky, but will mould together into a solid watertight lump after a few hours, 

[j_s]

Yep will do.

It might be hard to wrap the cables individually first , will see what I can do.

 

Do you think once sealed and the conduit is buried I should hopefully be ok?

[Jeremy Harris]

Should be fine once it's sealed up.  Wrapping the individual wires is important, as it allows the tape to bond together in between the wires, sealing up those tiny gaps between the wires.  A few wraps around each wire at a point where you can over-wrap the whole bundle with self-amalgamating tape, running the over-wrapped tape back to the tape over the end of the conduit, will ensure a good seal.

[ToughButterCup]

I expect there's a good reason not to use something like Illbruck airtight foam......

[Jeremy Harris]

9 minutes ago, recoveringacademic said:

I expect there's a good reason not to use something like Illbruck airtight foam......

 

Might be OK with cables, might not, I'm really not sure whether it would react or not.  My guess is that it may be OK, but I'd play safe and stick with self-amalgamating tape, as I know that's compatible with pretty much every type of cable sheath around.

[j_s]

Ok thanks guys, much appreciated