PIR- water resistant?

[zoothorn]

Reason I ask, is I drive past a stack of ~70mm PIR sheets left outside/ abandoned probably 6 yrs min at a guess. could it be used I wonder even trimming the obviously weathered edges off? obviously I can't just nab it & find out (I guess weight would simply tell you if water trapped within).. it is on s'one's property.

 

I can't think its made like a sponge, if its got to contain heat/ Id have though it be 1000's of tiny bubbles.. ie sealed. My builder's used some scrappy offcuts on my knock-through door (old stone cottage/ alot of pesky bits to fill) prety sure these been outside in elements.

 

Any ideas? cheers zoot.

[MikeGrahamT21]

This may answer your question? https://www.greenbuildingadvisor.com/question/polyiso-water-absorption-should-wrb-be-inside-our-outside-of-exterior-foam

[Stewpot]

It's what they call 'closed-cell' , which means that all the little bubbles are isolated from each other. That means it doesn't absorb water to any significant degree. I think there's a standard immersion test, where they hold a sample of the stuff under water for a period of time, and it has to absorb only a small fraction of its volume - something like 2% after a month's continuous immersion.

 

There may, however be an issue with UV light, as that does cause it to go a little crumbly.

[nod]

When I buy it in it’s often cheaper to over order It’s often left outside for 12 months Always gets used or someone takes it at the end of the job 

[zoothorn]

Ah thanks @Stewpot hadn't thought of its crumblyness. That might mean terrible cutting numnums.

[Stewpot]

18 minutes ago, zoothorn said:

Ah thanks @Stewpot hadn't thought of its crumblyness. That might mean terrible cutting numnums.

 

If it's the foil lined stuff, it'll probably only be the edges that are affected - you should be able to trim it off, but then you'll end up with slightly undersized panels. Though that may not be a problem to you.

[zoothorn]

25 minutes ago, Stewpot said:

 

If it's the foil lined stuff, it'll probably only be the edges that are affected - you should be able to trim it off, but then you'll end up with slightly undersized panels. Though that may not be a problem to you.

 

 Well this is what I was thinking. Yes its celotex I think, about 12  eight x four sheets stacked neatly in a pile. I'm gonna have to cut 8'x4' up anyway into 3 maybe 4 long strips (to insulate timber frame walls, studs ~400mm centres). If I could establish for definite only the edges might be n/g, & buy this lot off the hick.. I might well be able to save £500 who knows.

[Seeoda]

Some allege that it soaks water and reduces its effectiveness and hence should not be used as floor insulation.

[George]

On 12/01/2021 at 13:55, Seeoda said:

Some allege that it soaks water and reduces its effectiveness and hence should not be used as floor insulation.

 

PIR insulation should be above the DPM anyway.

 

Only time it's a concern in the floor is during concrete curing - wise to tape or stick some polythene over the top to protect the insulation for the ~24 hours of initial cure time.