Vapour impermeable sealants

[Peter Thompson]

Our supplier suggested that as we had to completely line our SIPs kit with PIR, once the joints had been foil-taped we would effectively have created a continuous VCL.  I'm aware that there could be flaws in this approach, but we're doing it anyway.

At wall and roof junctions it's tricky to tape properly using foil tape, and using a decent airtightness tape, especially one made for corners, would be incredibly expensive.

 

As the PIR junctions are very neatly done (I used an insulation saw), I've experimented using Soudal Vapourseal from Toolstation.  It's very slow to dry, but is supposed to be water and vapour impermeable and is economical and very easy to use.  It's now out of stock and likely to be discontinued by them.  Looking at intumescent sealant, it seems to be the same chemical formula...and is also an acrylic sealant that doesn't pass vapours.

 

Are there any opinions on this, and has anyone used a similar product for vapour sealing.

 

[Iceverge]

Airtighess tape need not be too dear.

 

 

You don't need the preformed corners, just a sharp knife and some practice it's not to hard to seal them up satisfactorily. 

 

Regarding sealants, something that remains permanently flexible is the aim of the game. The sausages are typically cheaper than the tubes too. Most generic acoustic sealants should be ok too but I've never used them personally. 

 

 

 

[Conor]

I'd foam any gaps, trim off, and paint on a liquid vapour barrier /airtight paint.

[Peter Thompson]

13 hours ago, Conor said:

I'd foam any gaps, trim off, and paint on a liquid vapour barrier /airtight paint.

 

I had a massive load of offcuts of the foam perimeter insulation for the screed. I had very few gaps in the insulation boards, but stuffed 10mm strips of the foam into all the obvious ones....the original definition of caulking. I'll look into liquid barrier, but the intumescent sealant seems to be ticking all the boxes and still gives me other options if I'm not happy with it.

[Onoff]

Illbrück FM330 foam is airtight:

 

https://www.illbruck.com/en-gb/products-systems/product-finder/fm330-pro-foam-air-seal/