Filling small (few cms cubed) spaces with expanding foam

[Chris Green]

I need to fill some metal conduits with something to prevent condensation forming and running out of the end. The standard answer for doing this is expanding foam but these conduits are too small for this to be practical.

For example one of them is about 2cm x 4cm cross section and 40cm or so long. It has some (12v) cables running through it so there's not a lot of 'air' left. At the moment both ends are open though the top end is a little inaccessible. I could drill holes at intervals to get access in the middle.

So, are there any products that will make it easy to fill this with something like expanding foam? A 'mini' expanding foam would be OK, with a tube 2mm or less diameter. ... or maybe something I can pour in, like potting compound, I can bung up the bottom temporarily while it cures.

[John R Walliker]

Are you sure that standard expanding foam would not travel down (or up) the conduit? You could attach the nozzle to the conduit with duct tape to allow more pressure to build up and drive the foam through.

John

[Andrew]

When an elec company do any jointing of underground cables using a splicing box, it has special plugs on top that they pour some sort of potting compound into, which is mixed with an activator immediately prior to use.

[Chris Green]

I have tried once and it didn't even seem to fill the end. It's difficult to make a duct tape seal as the conduit is flat against a vertical (steel) wall and is part of it so you can't wrap stuff around it.

I guess I could drill a series of holes down the conduit big enough for the expanding foam tube but that does feel a bit drastic!

[Chris Green]

Yes, that was the sort of thing I was thinking of, I can just about access the top of the tube. The 'stuff' would have to be quite liquid to pour down the conduit.

[Matthias Czech]

enough? But f****ng expensive. There must be cheaper brands.

[Chris Green]

This (drilling holes) sort of worked, I've made one hole and squirted expanding foam into it and it has filled a section. However it is rather difficult to avoid damaging the wires inside as the conduit is very tightly packed. I need a way to limit accurately how deep the drill goes and, given where this conduit is (and it's part of the wall that supports it), that's rather difficult.

[Theo]

The traditional approach is a rubber band around your drill bit: the drill stops when it hits the rubber band. It's hard on the rubber bands if doing many holes so you tend to need a few.

You can also get collars which have a grub screw and clamp to the drill bit. I have a set of countersink bits where the initial drill is the pilot and the collar is the countersink, but if you fit the collar backwards then the blade faces away from the surface and it acts as a depth stop.

Theo

[Chris Green]

I tried a collar but since it's steel I'm drilling the pressure required was too much for the collar to resist. There's absolutely no way a rubber band is going to help at all.

[Thomas Prufer]

How about taking an angle grinder and grinding a small flat on the conduit? With care, you might grind through the metal, and just scuff the insulation?

And maybe silicone sealant instead of foam -- more pressure on the cartridge (but less likely to expand along the conduit)?

Thomas Prufer

[Chris Green]

Yes, I have wondered whether that might be a possible approach. I'm currently exploring approaches from the ends, that may be enough with a flexible tube on the exanding foam aerosol. If I can seal both ends then that should stop water coming out of the bottom.

Yes, another possibility, thank you Thomas.

[SteveW]

I have, in the past, removed the Earth terminal from the back of a socket and used the terminal's own screw to clamp it onto a drill bit, as a depth stop.

[Theo]

I think you can get liquid silicone rubber - used for making silicone moulds and stuff.

One thing to be wary of with silicone is the cheap stuff is acetoxy cure, which means it emits acetic acid (aka vinegar) when curing. That can cause corrosion, so safer is neutral cure which doesn't.

Theo