EPS passive slab query

[Alexphd1]

While at a building show in Glasgow today, I was chatting to sales guy for a PUR passive slab. He told me EPS slabs was useless. 1. EPS shrunk. 2 EPS soaked up water.  3. When EPS was wet it had no insulation value. Somebody please tell this is wrong.....as my passive slab is on site. 

[Stones]

What was he trying to sell you?

[ProDave]

I thought it was the other way around and it was PUR that soaked up water?

[Jeremy Harris]

Well, in short, he's wrong on all counts!

EPS has been used underground in wet conditions for decades, on everything from railway track supports across bogs through to basement insulation in other parts of Europe to passive slabs.  One of the main benefits of EPS over other foams it that it doesn't absorb water, it's also one reason why you find so much of it washed up on beaches.  It simply doesn't soak up water, so doesn't change in U value appreciably under different conditions and it very definitely doesn't shrink when wet.

Some foams are not good in wet conditions.  PUR can soak up water and it's U value increases a lot when it does so.  Some PIR foams are also susceptible to water uptake, but primarily some of the older types (there are PIR foams that are rated for foundation use now).

[Alexphd1]

Isolohr.  He told me I had bought a expensive infill material!  

Edited May 22, 2016 by Alexphd1

[joe90]

As some of you may remember I am copying the Golcar insulated foundations and they specify xps insulation because the lambda value is better when damp. This is something I really need to get my head around as I am about to get my foundations dug!!!

[Jeremy Harris]

XPS has a better lambda damp or dry than EPS (doesn't change much for either, TBH).  XPS is also a LOT nicer to work with than EPS as it cuts more cleanly.  I've used loads of it for lost foam composite moulding, where the clean working is a significant advantage.  The only downside is that it is a bit more expensive than EPS and that it tends to have a structural "grain", in that it has a higher compressive strength along the direction of extrusion than at 90 deg to it.  Probably not worth worrying about for a foundation.  XPS is often slightly more accurately sized than EPS, as it cuts more cleanly when sliced from big block into sheets in the factory.

[Gone West]

I thought EPS was a generic term and that there are lots of various types with different characteristics. For instance my under slab insulation is Peripor which has high compressive strength and has very small granule size.

[Jeremy Harris]

EPS is specific in that it refers to Expanded PolyStyrene foam, but it comes in a wide range of densities and compressive strength ratings.  The number after "EPS" gives the compressive strength for 10% compression (too much "give" for a foundation) in N/mm², so EPS70 (the very light packaging type foam) is 70N/mm² at 10% compression, whilst the strongest stuff around is probably EPS300, at 300N/mm².

Some types have additives mixed in before the foam is steam blown, like graphite, which can improve the thermal properties and change the colour (this is often what makes some foam look grey, or have grey speckles in it).

It's all the same stuff though, in the sense of being the same type of plastic beads foamed in the same way with steam, that both creates the foam and bonds the beads together into a solid block.