Kingspan vapour barrier kitchen foil glue?

I have filled with kingspan between some studding, (on the inside of a stone wall with lime mortar) and foamed most of the gaps with pink drywall foam.
Now it needs a vapour barrier before I put the plywood back, to stop condensation in the wall from warm wet indoors air drifting outwards.
Someone suggested using aluminium kitchen foil for this: someone said plastic sheeting is not vapour-proof.
What sort of glue will stick the foil to the wood and kingspan?
Any better ideas andor advice please?
[g]
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wrote:

PVA
Plastic film resists water vapour passage, but not fully.
NT
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Tabby wrote:

yeah that's why you never see fizzy water in plastic bottles.
Just not waterproof.
Duh.

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wrote:

its why it goes flat in time in plastic. Its why some pills etc come in glass not cheaper plastic. Its why crisp packs are aluminised. etc. Anyone can look up vapour permeabilities. Or be foolish.
NT
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george [dicegeorge] wrote:

Since the plywood will hold almost anything in place you barely need use glue at all.
I'd avoid water based like PVA or wallpaper paste..didn't the kingspan come foil coated? in which case use the proper self adhesive tape...
or dot and dab the foil with hot glue maybe. *lightbulb* what about double sided tape?
Or use PVA and foil *the back of the plywood*.
Or cover the plywood with foil backed plasterboard?
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wrote:

Why? PVA loves aluminium.
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Tabby wrote:

Nowhere to dry out. PVA waterproof. Kingspan pretty waterproof. will stay soggy forever.
OTOH since its only got to not slide off while he screws up the ply..could be OK?
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The Natural Philosopher wrote:

Spray on Evostick. It's how I made few small sections of vapour barrier plasterboard out of ordinary PB.
Get a decent overlap on the foil edges and plenty of glue there. Sparing spray of glue on the rest of the area is more than sufficient.
--
Tim Watts

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I do just wonder if this isn't one of those situations where the passage of water vapour is so much reduced that the consequences of the minute portion that does cross the barrier is insignificant. My whole cottage had to have all the L and P plasterwork on the walls stripped off 20+ years, much as I think the OP is doing, rockwool insulated, etc., I just made sure that there was a large overlap between the sheets of polythene and certainly didn't bother about staple holes as they were into the strapping anyhow. Some of it was done 30 years ago now that I think about it, and there's no indication that I got it wrong.
Rob
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robgraham wrote:

There is no doubt that hot steamy kicthen and ice cold single brick wall is a recipe for condensation.
And that the better the insulation the icier will be the outside wall.
So its relevant. No one knows how relevant tho.

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Yes, but it's use is for vapour control, not for absolute waterproofing.

For a short period only.
Put liquid in a sealable container, put the container in a fridge or freezer and check weigh it from time to time and you will find it loses weight, surprisingly quickly.

You didn't make a case to rest.
FWIW early in my career I studied water losses from various sealed plastic packaging types. Polythene was only slightly better than Cellophane. The best packaging for my use - trying to keep a gel hydrated for about 10 months was a sandwich of polythene with a megapodes inter
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