I'd like to use some foam around a plastic downpipe, where it goes through a flat roof, but don't want to stick it in place. Can anyone recommend a suitable release agent to coat a piece of pipe with and mould the whole through the foam while it sets?
Cheers
Clingfilm?
Sleeve the pipe in plastic sheet first?
Owain
Bolted wibbled on Friday 27 November 2009 17:22
Grease the pipe. Vaseline should be good enough.
Or rather than cling film (which will stick in its own peculiar way) just wrap a piece of plastic sheet round and tape it in place.
Teflon baking sheet from Morrisons?
wrap it in clingfilm
Probably worth padding out with several turns, to increase the effective diameter a little so you don't end up with an impossibly tight fit. I would lightly oil the outer surface of the plastic. My recollection is that cling film stuck quite well to expanding foam, when I did some 10 years ago (although cling film isn't the same stuff nowadays).
The Natural Philosopher wibbled on Friday 27 November 2009 18:59
The Croydon Condom?
- You are probably using lead/aluminium flashing around it?
- The hole can be made to a suitable oversize within limits?
- Expanding foam cuts with a padsaw as easy as pie?
By padsaw I mean a handle with coarse blade on it.
Go buy a padsaw. Make the hole sufficiently oversize. Fill in with expanding foam.
If you really must have a future-removeable slip joint:
- Find another pipe which is oversize, expand foam that one in place
- Use a non-setting mastic between that pipe and the downpipe
An example would be 3M 08509 which is a non-setting butyl good (used on car windscreen seals, never sets, just forms a skin which is waterproof - comes in a sealant-gun style cartridge).
goo not good.
Use it between the outer tube and the inner tube, expanding foam the outer tube to the roof.
Silicone oil, or wrap it baking parchment which is usually paper with a silicone oil coating.
And expanding foam is degradable in daylight is it not?
In message , GMM writes
Someone post ... the link
What you talking about ..What link?
Aah - you'll have to wait until someone who knows cottons on to what I mean
Around the top outside. Around the bottom inside I assume he will have a ceiling. :-)
The problem is most pipes are not perfectly round, so anything that acts as a "release agent" needs to also provide sufficient clearance for the withdrawal of the pipe - not just prevent adhesion. Several layers of clingfilm would do it, but an issue is its longevity.
Using an outer pipe as a sleeve with non-setting butyl sealant in between seems to provide a workable solution. The flashing on the roof providing the waterproofing. It's about =A38.59 a tube plus postage - last I bought was 2007.
An alternative would be to use a "marine grommet", or "plastic roof flashing":
- Basically a cone of plastic or rubber with a square baseplate
- The cone is ridged at different circumferences allowing it to be cut to size
- It seals against the pipe via mastic or if rubber simply compression
They might exist on Ebay at a sensible price.
Look., maybe I am being obtuse, but if you want a removable pipe with a watertight seal, why not simply lay down a ring of silicone rubber round it BEFORE foaming in place?
But I must say 'removeable' and 'watertight' don't belong in quite the same sentence.
Another option if its waste pipe size, is to cut down a loo coupler with a rubber ring seal and welly that in place with the foam.
BUT it seems stupid to me. Make a big hole, foam in place and slip flashing over the lot. Then if the pipe needs to come out, remove flashing and use padsaw in foam to remove pipe, which goes in the skip. Its cheap enough.
My first time back here since I posted and this seems to have caused a disproportionate amount of consternation! So much for trying to be brief and not explaining the whole job....
The situation is pretty straighforward: A hopper set into the top surface of the roof, which covers the carport. Everything newly sealed etc etc. The downpipe makes a sliding fit around the tapered base of this, like all good downpipes should. The underside of the roof (carport ceiling you might call it) is plasterboard and skim. With various leaks, changes of downpipes etc over the years, the 'ole in this 'ceiling' has become a lot bigger than is right, and I'm looking to tidy the whole lot up. There are two things I could do: Fill up the 'ole (with a bit of squirty foam, allowing for the issues described in 'the link'), or fix a plate (a square of ply) on the ceiling with the right size 'ole in it. Either way, it would be a good plan to allow for the downpipe to be removed etc (if only to make it easier to paint behind). Clearly, either hole (in ply or foam) needs to be a bit bigger than the pipe to allow it to be slid out: Still haven't got a firm plan on how to do this for the foam (probably something a bit thick wrapped around it a few turns), but clearly it would defeat the purpose if it was stuck to the foam (and we all know how sticky foam can be!), so I need to find a release agent. My first thought was anything oily/greasy, but I thought I'd tap the wealth of experience here to see if there was a simple one-liner!
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